The difference between WA and GA is a little difficult to understand in the beginning. And being an English speaker, its even more difficult. I have passed the JLPT Level 1 exam and I still have problems and slip up often. As a beginner, all you can really do is learn from seeing and using. I'll just assume you know 好き is an adjective, so I won't go into why を isn't (rarely) used. For 好き, が is almost always used. As to why, a sugar-coated answer can be that its the subject of the sentence, its emphasized, and it and it specifically is what you're talking about. 像は鼻が長い。 Zou wa hana ga nagai. Elephants have long noses. You're talking about an elephant, but specifically their noses are long. リンゴが好き。 (I) like apples. Not bananas, not peaches, apples. The emphasis is on WHAT you like. リンゴは好き。 (I) like apples. We're now going to have a long discussion about apples, and to start with, I like them. EX: I like apples. Their color is red. They are grown on trees. Someone choked on one. I didn't like them before... It'll probably be hard to get a grasp, but が is usually used when focusing on what the subject of が actually is, and は when the rest of the sentence is being looked at more. 誰がケーキを食べたの？ Dare ga ke-ki wo tabeta no? Who ate the cake? WHO is what you want to know. JOHNが悟史を蹴った。 John ga Satoshi wo ketta. JOHN kicked Satoshi. JOHNは、悟史を蹴った。 John wa Satoshi wo ketta. John kicked Satoshi, among other things he did. Sorry for my long drawn-out response. Hope it helped a little! And anyone, please correct me if I'm wrong. I'll be embarassed but very grateful!