You know that 「が」is the subject making particle but its second function is the particle which puts stress on the object.

For example:

ケンタはミカがすきです: Here the speaker want to say,  Kenta loves not the others, but  MICA.

私はすしがたべたいです。The speaker would like to eat not udon, soba or steak, but SUSHI.

Good luck!