Champions available in League of Legends
Good afternoon Arti Schmidt!
League of Legends has a different system for new players, which means in the first few (5 if it is still the same) levels you will have a specific champion rotation available. After those levels you will have the normal free rotation. You can read more details here: League of Legends Starter Champions - Article at RockPaperShotgun or here: League of Legends FAQ (almost at the bottom of the page).
Best wishes, I hope I could help!