If you want to know what the exit looks like, simply enter the backrooms and look behind you; This is what the exit looks like.
But you might notice you cannot exit through here, this is because you cant exit through the entrance, because that would be too easy would it? If you are brave enough to explore the backrooms in hopes of making it out alive then Here is how you find the exit.
When wandering through the backrooms you will notice MANY and i mean LOTS of twists, turns and dead ends. Some super smart person may be able to decifer the random level generation to make it easier to find the exit but until then you must know that each face of the wall has a chance to be the exit.
For example, you find a wall pretruding from the level, you can see that it has two sides. If this wall does actually have the exit. You wont know until you check each face of the wall. One face of the wall may be normal, but the other side may be the Glitchy blurry and freaky looking exit we hope to find.
When looking for the exit, dont bother looking around until you wander a while into the backrooms.
The exits dont apear close to the entrance.

When you are lucky enough to find the exit, its not over yet. Walk over to it and press your Interact button, or E as most people will have it. A UI will appear, it will seem to be a white line and a beating heart in the middle, a dial should be moving through the line. Press your Interact Button
when the dial is over the heart, succesfully doing so will calm you down and hopefully allow you to exit, if failed, you will go mad, more on that later.

Escaping through the exit is actually the easy part, Surviving long enough is the hard one.
We will start with the basics, You have a watch, every 30 seconds you will be prompted to press E or your Interact button , Doing so will calm you down, keeping you sane. Checking too often will increase your madness.
Even though you may be tempted, do NOT look at the lights, this will make you go insane, just keep your head down.
Dont look at it , when wandering through the Backrooms God forbid you hear it, because it sure as hell heard you. The monster is a black figure you may encounter if wandering the backrooms long enough. being near it will make you go insane, looking at it will do so faster than anything, and it makes a static noise, run from that noise.
while on the running topic, running will make noise, drawing the being closer to you, use it sparingly.

As you can see in the image, the lights are off, this is one of the many consequences of going mad.
others are things like the floor shifting beneath you, Distorted screaming and footsteps, crying and your vision getting blurry or different colours.
How ever if any of this happens, its not game over, check your watch and remember who you are.

If you go mad, well i think its safe to say that you will most likely have no chance of escaping