You can sign up for the beta at the official site (via Polygon), which will allow you to build your own kingdom and collect studs to gain new weapons and armor. Any progress you earn in the open beta, including bricks, powers, and items, will transfer to the full game when the beta ends. The free-to-play hooks come in the form of premium currency, but Warner Bros claims that it isn't necessary to progress.
Lego Legends of Chima: Speedorz, a racing game, has been out on iOS for several months. The third announced Chima game, Laval's Journey, is currently in development at TT Games.