Since I started to study Japanese, I found this difference pretty difficult to understand. Even my teachers (japanese) could explain only partially how actually they are used. Anyone?
"が(ga)" emphasizes the word just before it.
When you pronounce the sentence ,
you should put the accent on "が(ga)" together with the noun before it.
Below are examples :('' indicates the accent )
'Aitsu "ga"' warui. = 'HE' is responsible for it. (Answering to "Who's done such a bad trick ?")
Aitsu "ha" warui. = He is an 'EVIL' person. (Answering "What kind of guy is he ?")
'Kore "ga"' suki. = 'THIS one' I like . (Answering "Which one do you like ?")
Kore "ha" 'suki' = Yes I 'LIKE' it. (Answering "Do you like this ?")
'Watashi "ga"' yaru. = 'I' will. (Answering "Who will do it ?")
Watashi "ha" 'yaru'. =Yes I 'WILL'. (Answering "Will you really do it ?)