The TFT Ranked Queue works a lot like the one in League of Legends. There are nine tiers from Iron to Challenger. Finishing in the top four counts as a victory and will earn you LP. If you place in the bottom four you’ll lose LP. The extremes, first and eighth, respectively, will have a bigger impact than if you place in the middle of the pack.
You’ll need to complete five placement matches before being put into your respective tier. The good news is that there are no promotion or demotion series. Hit 100 LP and you’ll go up a tier. Hit 0 LP, then lose, and you’ll go down.
Of course, Riot is putting some restrictions in place regarding who you can and can’t play with. For example, someone in Platinum can’t queue with anyone in Iron, Bronze, or Silver. Check out this handy chart for the full details;