As you use innoloop, you will be awarded points for adding your Ideas, Comments, creating new Challenges and when other people appreciate Ideas that you have added. Achievements will be unlocked each time you pass a milestone in each of those events, for example you will be given a new Achievement once you have added 5 Ideas. You can see what Achievements you or others have unlocked by Viewing profile pages. From there you will be able to see when each Achievement was unlocked.
The Leaderboard adds some friendly competition by showing how many points each person has, clearly illustrating who is contributing more and recieving more appreciations. If you want to climb the Leaderboard, then start adding great Ideas and contributing to other Ideas by adding Comments to them.