If you aren't a competitive battler, you will get crushed. Anyway, PO stands for Pokémon Online, an online Pokémon battle simulator. No, it's nothing like Crater or Lake. PO is built only for battling. You can build your own team from scratch. Any level (100 max), any moves (legit of course), and adjustable EVs and IVs. So there's no need to train. Just build your team and battle. The battles on PO have saveable battle logs in case you ever need them. IRL, an online battle can take 10 minutes or more. Whereas a battle on PO takes only a few minutes most of the time. Anyway, check out the site:
Pokémon Online
EDIT:
Ninja'd. CURSE YOU!!!!!!
Pokémon Online
EDIT:
Ninja'd. CURSE YOU!!!!!!