A standard League of Legends Fantasy League in Sleeper is composed of 8 Teams. When you create or join a league, all Teams will be empty. Each Team must be assigned a Manager.
A major highlight of Fantasy Sports is the virtual general manager aspect of owning and managing a Team. Fantasy Teams are made up of Professional Players, whose real-life play affects the outcome of your Team's weekly results.
Teams will compete against one another head-to-head, throughout the season, based on a predetermined schedule. Each Team's weekly score will be based on the actual performance of their Pro Players and respective Champions during the LoL Tournament play.
Just like in real life, Teams in LoL Fantasy, have a starting Top, Jun, Mid, Adc, and Sup roles/positions. You'll want to fill out your Team via the Draft and the use of Waivers/Free Agency.
Managing a team is half the fun of playing Fantasy. As a manager you'll get to Draft your Players as well as change them as desired, using features like Trades or the Waiver/FA Pools. Each week you'll want to set the optimal lineup based on how you and analysts believe Players on your team and Waiver/FA Pool might fair, week-to-week.