Hey there Tom, welcome to PokeCommunity :D I'm not into battling, but I can redirect you to the
Battle Center. There you can get advice on how to build teams and look for battles and tournaments. I am, however, interested in trading, you can usually find me hiding inside the
Trade Corner. Here you can find some guides, discussion, and people to trade with. I'd also recommend you check out the
Fifth Generation Games forum. There you can discuss and ask questions about the Gen V games. Are you looking forward to or planning to buy X and/or Y? If so, the
Pokemon X & Pokemon Y forum is something you should check out, you can discuss, speculate, look for news, and what not with other members here.
If you have any questions, feel free to ask me or a staff member here. Alternatively you could also post your question in the appropriate forum here (and in the appropriate thread if necessary), just make sure you read the
PC Rules and rules of each forum you go to. It helps to prevent any accidental rule breaking in the future. I hope you enjoy your time here at PokeCommunity!
EDIT: As mentioned by Cirno, most people battle over Showdown, but there are a few people who do Wi-Fi battles over at the
Quick Battle Requests. There are also some people who still do them over at the Trade IRC channel. You can go
here to learn a little more about it.