Ummm... you can only spend an hour in it per day. It's random where in the dream world you go when collecting pokemon, you have three areas to start with and you unlock a few more when you earn enough points. The different areas have different pokemon in them, you find them and if you want to "catch" them, you play a mini game and if you don't totally suck you can keep them. You can only take one pokemon per day.
...I hope that made sense. It explains everything to you the first time you do it, so it's really not complicated. lol