This guide assumes the following:

• Either you planned an IFR flight in the main menu (Low or High Altitude Airways), which will provide you with a flight plan which should mostly be flown automatically, or you can follow the next section to manually set up the plan in flight via the onboard computer.
  
• You know the basics of the Airbus A320N autopilot and used it to follow your flight plan to the designated arrival airport as normal. You should know how to follow flight plan waypoints, use managed and selected altitude/heading/speed mode, use the autothrottle (we only need CL and go to zero on ground contact) and find basic information on your nav display using the scaling and mode knobs.
  
• You know how to contact ATC, ask for permission to land and make use of it. ATC communication is not fully covered by this guide. (The ATC window is kinda self-explanatory) Note that you might need so specify that you want an ILS approach.
  
• You didnt input any values into the MCDR (input panel with keyboard above the thrust lever) yet.
  
• Your designated arrival airport supports an ILS approach.
  
  Don't panic - this is not as difficult as it seems. Also, the worst thing that could happen is that you could crash and die along with your crew, passengers and people on the ground.

You can skip this step if you planned an IFR flight in the main menu and intend to land at the designated arrival airport. If not, you can always do this step in flight.
(sometimes, IFR flight plans lead to glitches with the ILS systems in Flight Simulator - this step can potentially eliminate them)

Go to "Plan" mode to view the route on your nav display to confirm your waypoints in the next screen. This enables the nav display to center selected waypoints as chosen in the MCDU (the small computer with keyboard above the thrust lever, also known as FMGC). Adjust scale if necessary.
Go to the MCDU and press "F-PLN" to open the flight plan menu.
Select your destination waypoint at the bottom and choose "arrival"

"APPR" should show "ILS [designated runway]"
"STAR" (Standart Terminal Arrival) should show a waypoint which grants you entry to your approach vector.
You can change the runway below. If you do so, a yellow line on your navigation display should indicate the selected route you could select.
Use the arrow keys below the MCDU (arrow left) to select your STAR.
"VIAS" would be additional waypoints along your route. It is not unusual to have none.
Final Approach Heading shows you from which direction you will land on the runway.
Press Insert so prime your selected approach.
Your Nav display should now show a green line.


Check your instructions to the flight computer by selecting
"F-PLN" and scrolling to the bottom.

Go to "RAD NAV" (Radial Navigation)

You can see the ILS Frequency, which should be automatically tuned in. In a real A320N, you would have to do this by hand and use an external source
(SkyVector (free) for us airports is a good source for hobby pilots. A real pilot would likely use NaviGraph. These frequencies can change and might not always be up to date in Flight Simulator, although it is fairly accurate.)



Manually tuning the frequency is done via the MCDU on the "RAD NAV" display, but it is possible to to it via the Radio Panel (beginning below the MCDU keyboard) as a backup.

The autopilot needs some basic information about the airport, which you can get from ATC.
This will allow it to fine tune the approach, although this shouldn't be needed for most cases.
(A real pilot usually does not skip this step.)

Once in Range of the Airport Radio Stations:
Tune ATC to ATIS (usually there will be two frequencies, one for arrival and one for departure) of the designated Airport, get local weather information.
Go to the MCDU (the small computer with keyboard above the thrust lever, also known as FMGC).
Press Perf and choose "Approach" phase. Enter the weather info you just got via ATIS (QNH - the altimeter setting, wind, temperature).
Optional: Set Minima - the minimum height during approach where you need to have visual to the runway or reference lights. If you do not know the minima for your designated airport, there are several external sources you can use, examples stated in the section above. Guessing or skipping also works. Flight Simulator currently does not provide you with these values afaik.

Set your altimeter settings to the value you got from ATC. (the same value you put into the MCDU)

Choose constraint mode for your Nav display to get a rough idea of your altitude restrictions.
These are shown next to each waypoint.

If you want, you can check the next phase, which will be the "go around" in the MCDU.

If you skipped the step above, set your altimeter settings to the value you get from ATC for your designated arrival airport and choose constraint mode for your Nav display to get a rough idea of your altitude restrictions.
These are shown next to each waypoint.

Switch on the ILS info by pressing the LS button (below the altimeter, left from autopilot). Yellow reference lines and a diamond shaped indicator will appear next to your primary artifial horizon to show the direction the the active ILS waypoint, similar to the flight director for normal waypoints.
Select ROSE LS Mode on the nav display turning knob.

Currently, it is possible to get some waypoints which the plane might find difficult to follow (mostly because there are too many of in close proximity to each other). It is expected to get improved via the next patches soon afaik.
Even though in real life this would usually not occur, there is an option to circumvent this.

In this case, you should skip to a waypoint close to the glideslope at your own discretion (final approach)

Press DIR in the MCDU and choose a ILS waypoint to skip until this point.

When close and facing the airport, press APR (Approach) to engage the glideslope. This will arm both the localizer and the approach. The localizer alone would not control your descent, as it only allows for two dimensional navigation.
Check in the MCDU Perf Screen if the approach phase is set, or manually choose it.
This will ignore all other waypoints.
"G/S" for glideslope next to your artificial horizon will indicate that it is armed (indicated blue), and later active (indicated green).
Same should apply to "LOC" for localizer.
Ident marker in the bottom left of the primary artificial horizon when close to the runway should show a succesful lock onto the ground based ILS components.

I suggest use of managed speed mode here, but keep an eye on the autothrust performance.
Be aware of the flap speed limits when setting the flaps. (Yellow markers on the speed indicator next to the artificial horizon.)
Maintain CL on the thrust lever.
Check the flight path. If needed, adjust with heading mode.
(At this point, you could set your autobrake settings. This will engage wheel brakes on contact to ground.)

These rules of thumb work on clear days.

This is where everyone should be in a brace position your work pays off.

Regularly check speed, altitude above ground and the window ahead of you if weather conditions allow you to see runway reference lights

On contact to ground:
Check plane alignment as often as possible.
Keep an eye on your speed and abort landing if needed.
Pull thrust to zero before the front wheel contacts the ground.
If you dont use autobrakes, manually use the wheel brakes.
Engage Airbrakes if needed. Correct with rudder. (You can still use it while the A/P is active.)

At around 60 Knots or whenever you feel comfortable, you can disconnect the A/P and manually taxi off the runway.
Use rudder (wheel turning) on the ground to keep the plane steady on the runway, do not come to a full stop and clear off the runway on the first occasion. Contact ATC for further instructions.