Understanding user "trust levels"

Let’s Talk Pitching has five user trust levels, and your current level is visible on your user page:
0 (New) → 1 (Basic) → 2 (Member) → 3 (Regular) → 4 (Leader)

As you contribute to the forum, you rise up through those trust levels.

New users (at level 0) have limited functionality; the more you participate and contribute positively, the more functionality becomes available.