The top level is SM Liiga, where the best players play for the Finnish Championship. You can read our prejudiced opinions about the SM Liiga clubs in the ‘Introduction to SM Liiga’ tag, if you like. As to format, well the Wikipedia entry on SM Liiga is good, but this is all to change next year. The number of games will increase from 56 to 58, and there will be one fewer game against the ‘designated’ clubs.
Unlike in football”s Veikkausliiga, there is no automatic relegation. There will also be a play-off involving the bottom clubs, with the 11th playing the 14th placed team and the 12th playing the 13th. The losers will play each other, and then the losers of that game will then play the winners of Mestis. If the Mestis team wins they will have the opportunity to buy a share in SM Liiga (ie get promoted) for an as yet undetermined price. This is a good analysis of the changes.
Below SM Liiga is Mestis, then Suomi Sarja, then the regionalised leagues. Finland has 52,000 registered hockey players, and they all play for someone….