Excellent link Kelly!
Tarah please feel free to join in. You don't have to go back to January. Just start whenever. Project life is about documenting your life (everyday moments that maybe you wouldn't do a full 12x12 layout about). Little things like meals, accomplishments, things your kids say or do. You can add in trinkets, ticket stubs, random pictures, etc. There doesn't have to be an overriding concept or theme. You can do daily entries or monthly entires or just whenever- no rules. It is like a "peek" into your life.
Just google Project Life and tons of inspiration will come up. The most common pocket sizes are 3x4 and 4x6 but they come in many more. And you can make it your own and do it the way that you see fit.
The girls here have wonderful examples. Everyone has their own unique process/outcome.