Learn Finnish: He eivät tykkää jääkiekosta.

The verb tykätä (to like) always requires the thing you like to be in the elative case. This case ends in -sta or -stä (which normally translates to "out of" or "from"). When speaking Finnish, you literally say you get enjoyment out of ice hockey.

The dictionary form is tykätä with one "k". Why does tykkää have two?

This is due to consonant gradation, which happens in verb type 4 words like tykätä. When you conjugate it into the present tense or form the negative stem, the "weak" single k strengthens into a "strong" double kk.

If the subject is "they" (he), shouldn't the verb be tykkäävät?

It would be he tykkäävät in a positive sentence ("They like"). However, in a negative sentence, the negative verb takes the ending (eivät), and the main verb just uses its negative stem without personal endings. The negative stem of tykätä is simply tykkää.

I know jää means "ice". What does the kiekko part of jääkiekosta mean?

Kiekko means "puck" or "disk". So the base word jääkiekko literally translates to "ice puck", which is the Finnish word for the sport of ice hockey.