Welcome to Rescreatu, Majick! The site can definitely be a little confusing for new players - there's so much to do! If you're a Rancher, you can open a Rancher shop and sell Creatu - natural coloured creatu don't sell for much unless they have really good names, but coloured creatu (especially Blonde and Albino) sell for a lot more. Make sure to use up all three hatches every day so that you have the best shot at those rare colours!
If your a merchant, I don't have many tips (I'm a Rancher myself). But a good way to bring in a bit of tu is to to buy Super Healing Potions from the pharmacy - buy them for about 800tu and sell them for 2000tu-5000tu, and you'll bring in a steady flow of money.
Whether you're a Rancher or Merchant, you can train and battle your pets, play games, chat in the forums, display creatu in your show rooms, etc. There are some shops that you can't view, depending on which planet you chose, and there are some creatu that aren't avaliable anymore or at the moment (Omni, Kioka, Liyure, Ebilia, Iluvu,etc) these creatu only come out at certain times of the yea, or have retuired from the cash shop.
I can't think of much else to say! I hope you enjoy it here ♥