As people play League of Legends, they eventually unlock Ranked Mode. This is a normal game of 5v5 on Summoner’s Rift. This is ranked however, so wins and losses with affect your ranking. After your first 10 games, you are placed in one of the following divisions (low to high): Bronze, Silver, Gold, Platinum, Diamond, Master, and Challenger. Each division up to and including Diamond have 5 tiers to split up the skill range further.
To go up in rank,you must first gain 100 LP, which is gained by winning matches and lost when you lose matches. After reaching 100 LP, you get a promotion series, which is either a best of 3 or best of 5. Winning this will promote you to the next division or tier!
The most common division for a player to be in is from Bronze to Gold, holding almost 90% of players! From there it quickly drops off with about 8% of players in Platinum, and 2% in Diamond, with less than 1% of players in or above Masters division.
The process for reaching Master or Challenger rank is calculated differently. The top 200 players are in challenger rank, refreshing every 24 hours, making it extremely competitive to be Challenger rank. The rest of the players are in masters unless they are demoted to Diamond or promoted to Challenger.
If you don’t play ranked games for a long enough period, your rank will start to decay, meaning you lose LP over time which will in turn drop your rank. This prevents people staying at a high rank by not playing.