How do I know if I’m entered into the contest

If you open the contest, under the badge on the upper left corner, there will be a gray bar that either says Join Now or Withdraw, that will tell you if you are entered.

Most you have to click join, then select a qualifiying diary or picture etc... your name will be in the list after that. The grow questions will automatically put you on the leaderboard when you get a solutions awarded from a question with a diary attached. (no diary attached = no points). It'll show a link to the diary with a picture labeled "Week X", if it has one attached. If you can't join a contest, read the rules for that contest and it should clear things up.