좋다 is not a contraction of 좋아하다 but it can translate as both like and good in English. - 이 음식은 좋다. (This food is good.) - 나는 이 음식이 좋다. (I like this food.) When 좋다 is used in the meaning of like, it always takes the sentence structure of "은(는)" ~"이(가)" 좋다.

할아버지, you can use 좋아한다 if the sentence what you want to convey has 'object'. Consider the following please: Somebody likes something.(Subject+Verb+Object) I like Greek salad.[나는 그리스식 샐러드를 좋아한다.(Subject+Object+Verb) I like Greek sald.[[나는 그리스식 샐러드가 좋다.(Subject+Object+Verb)