In a sentence
りすsquirrelはどんぐりacornが好きlike
Squirrels like acorns
How it works
好き (like) works differently from the English verb “like”: it’s really an adjective meaning “liked/pleasing.” So the thing that is liked gets marked by が (subject), not by an object particle. は (topic) sets up who we’re talking about (りす (squirrel)), and が (subject) points to what pleases them (どんぐり (acorns)). Literally: “as for squirrels, acorns are pleasing.” No copula needed, so it stays plain and casual.