Like any Parklife park, you start by creating the Main Building where skiers will enter and rent skis. From there you can create your paths out the back to the skiing area; nature reserve paths work well, or grab an invisible park path from the workshop. A Lodge nearby is always welcome for rest and relaxation.

You'll need to create a Chair Lit Base Station [cable car end station] nearby to get up the mountain. At the top of the mountain, place your Chair Lift Summit Station [cable car end station] and connect with the lift cables [cable car cables]. This will get your tourists up the mountain. [Best to place on completely flat ground first, then Move It! as needed to prevent any weird height issues with the pillar sub-building.]

Next, place your ski trails (invisible bus roads) from the Chair Lift Summit Station and down the hills back to your chair lift terminal. Get creative, but don't intersect trails – use anarchy to overlap if you need to cross paths rather than intersecting as junctions will potentially alter the pathing of the skiers.
Pro Tip: It can be helpful to use an actual road as a visible guide at first and then upgrade to ski trails after. Force elevated mode (Fine Road Tools) to prevent ground flattening; when using elevated mode, segments can path above/below ground level between nodes - adjust nodes manually so skiers stay at ground level!

Connect the ski trails from the Chair Lift Base Station at the bottom back to the terminus at the top by using tunnel mode. Make your entry and exit points as close to the skier loading/offloading spots as possible. Skiers will pop in/out of the ground at this spot but it's the best I can do without modding.

You should now have a complete ski trail loop. Create additional ski trails as desired; connect all to the return tunnel and split off at the top.

Back at the top of your mountain, create a Skier Staging Area (sightseeing bus terminal with 4 stops) and Skier Spawn Point (1x1 sightseeing bus station) near the Chair Lift Summit Station. These both need to be "roadside", so place along your ski trails. Create a sightseeing bus route from the Transport > Tours menu, and create one stop at the Skier Staging Area and the other stop at the bottom on the ski trail near the Base Station, and finish the line back at the top.

Using Improved Public Transport 2, skin your new sightseeing bus route to use the Skier or Snowboarder options (1 person sightseeing bus) and make sure the depot is your Skier Spawn Point. You can also choose how many skiers/snowboarders you want on each trail.

Place Ski Lights, Rescue Towers, and Snow Cannons around the slopes to boost attractiveness for the sightseeing routes on your new ski trails, making people more likely to visit.

Viola! Tourists will now come to your Ski Resort, take the Chair Lifts [cable cars] to the top, ski down the mountain [sightseeing bus tour], and then relax at the Lodge. The best part is the Skiers have the snow particle effect for vehicles and throw snow up behind them like Snow Plows, so they look like they're really skiing!

Known downsides: Unfortunately cims are not dressed appropriately for a ski resort without official/modded implementation. Also, the chair lifts are empty on the way up since there's no differentiation between trips up and down (can't have a cable car model with people on it going back down, so all lifts have to look empty instead). If CO were to make this into an official game mechanic, it would need to be a ski resort district where cims would be dressed for winter, ski on ski trails, and ride up the lifts but not back down.