Silan is an island where homins emerged after many years of 'exile' in the Prime Roots.
This is where all characters start out in the game. Since Patch 1.5.0 a subcribed account is no longer needed to leave Silan.
Silan contains many different people with which the player can interact with, above all a trainers for fighting, magic, harvesting and crafting, mission givers for both factions the Kami and the Karavan and a set of missions for the Rangers. All missions given on Silan act as a tutorial for Ryzom i.e. Silan should not convey the idea that Ryzom as a whole is quest-centric.
For a more indepth look into missions and tutorials on Silan see Silan Guide.