This guide is climb oriented. There are a lot of other ways to play the champion and have fun but i have the most success with this way of playing.
General information
Yorick excels in splitpushing and teamfighting because of his ultimate which basically gives your team an extra person the enemy has to adress. His tower taking potential is quite high even in the early levels which can be abused to get a lot of plating.The champion is immobile which means you need to expertly use your w and e to compensate for that fact. The q+passive is quite an amazing tool because it gives you sustain on top of the damage. Usually earlygame its best to use it to get graves instead of poking because the ghouls would do a lot more damage if you manage to unleash them on your enemy.
Early levels
Try to get lane priority and push the wave under tower with the help of ghouls at around wave 3 or 4 so you can get a cull or a long sword and come back to a wave thats pushing to you.
Mid and late game
You want to be creating as much space for your team so they can do objectives and get better teamfights. Dont overpush unless theres a dragon/baron spawning or already in the map, you want to have your maiden up and running as much as possible because it creates maximum pressure and kill potential for you. Dive enemies under tower you do have the damage to force them off towers or kill them, or ignore the enemy to get the tower and then fight them if you can take the tower quicker than he can inflict a lot of damage to you.
Maidenless
You are at your weakest when you dont have maiden up so try to just get the graves up to 4 and dont take as many risks like aggresively pushing because your pressure is quite low just focus on getting more gold and keeping yourself alive.
Maiden
you can push up to 2 lanes with maiden up as long as you create ghouls in a lane and they attack the minions they will keep pushing it so you can leave or tp to another lane and create maximum pressure so your team can get objectives or maybe just a better teamfight and even if your entire team gets wiped you will have bought time for them to get back since the enemy team needs to send 2-4 people to adress your splitting. Taking fights with full ghouls+ maiden ensures the enemy cant stop you 1v1 and more people are needed to adress you. Dont be affraid to dive them mid and late game you should have the hp and damage to pull it off or at least push them off that tower so you can take it.
Weakest against
Champions that can dash out of your w but even then you can w yourself and kite in and out of it while you are doing damage they will have a harder time hitting you.
Strongest against
Immobile champions and champions that cant dash through walls since you can make them stuck and force a flash or a kill out of them or in defensive cases just save yourself from dying or flashing.
