Experience in this game will be granted for four things viz:

Participation.
Each and every post made earns you 10 xp. Since the game tracks posts, this is easy, just multiply your 'number of posts' by 10.

Choking.
Failure can teach us more than success, or at least encourage trying not to fail in the future. A simple failure is worth 10 xp and a critical failure (a jam or botch or by more than 5 degrees) is worth 25xp.

Pain.
Pain teaches very quickly. Each Wound or level of Fatigue is worth 10 xp. Critical damage is worth 25 xp per Wound (assuming your character survives it natch). Fear also falls into this category, and damage avoided by cover or armor or Toughness bonus is worth 1 xp each. Note that being Pinned or suffering Shock falls under 'failure' above.

Roleplaying.
Playing your character well or meeting character personal goals or cell goals is worth xp subjectively awarded by the GM.