The Women’s Flat Track Derby Association has links to the Rules of Flat Track Roller Derby in several languages.
The Junior Roller Derby Association has an Addendum with modifications to the WFTDA rules for junior derby.
JRDA divides skaters into four levels: Levels 0 (beginners), 1 and 2 are still learning skating and derby; level 3 skaters are proficient. Each level has a separate set of required skills, and a separate skills assessment. Here are the Skills Assessment forms.
Some other useful resources for beginners:
WFTDA “This is Roller Derby” beginner skater curriculum
WFTDA one-page PDF of Roller Derby Basics
WFTDA Online Education Series: Roller Derby Skills YouTube playlist: