Hey
tinywretch, welcome! B101 is indeed more aimed towards intermediate players and you should start by trying to get the basis of the game. I don’t know how new to comp Pokemon you are, if you're still not familiar with stuff like IVs/EVs and main game's mechanics I would advice searching for guides on youtube as there's plenty of very good ones to understand how all this works. Once you have this first knowledge about the game (if you don't already have it), picking a tier and trying out sample teams is the way to go. Though, you will indeed have troubles finding out how to play these teams at first and there's other ressources you can use.
First one is the smogdex where you can find a bunch of analyses for most Pokemon in most tiers. They may not all be up to date, but they can help understanding how each Pokemon works, what does it beat, what type of sets it can run... Here is the main smogdex page:
https://www.smogon.com/dex/ss/pokemon/ (you can filter by tier and Pokemon).
Another great ressource is the tier subforum here on smogon and especially some threads like the Viability ranking which help understanding what works well in the tier (for example here is the ou one:
https://www.smogon.com/forums/threa...ranking-thread-see-page-90-post-2242.3674058/).
Lasty, you can try asking for feedback on your game with replays in PS rooms like the room of the tier you are playing or the Trainer Academy room (kind of b101 for PS). You won't always find someone willing to review your game but some people may accept to help and give you advices.
Once you've gather some first knowledge in a tier, then yeah b101 is a good place to get even better. Hope this was helpful, my PMs are open if you want to talk more about all this or if you have questions, have a nice day!