A little bit complicated, actually. We can understand the using of particle by using it on a sentence. For example: Ito-san wa chiketto wo haratte imasu (mr.Ito is paying the ticket) Ito-san ga chiketto wo haratte imasu (it is mr.Ito who is paying the ticket) There is still many form of "ga" and "wa" which is totally different. For example: In basic lesson "wa" usually followed by verb: Obasan wa nakimasu (aunty cries) While "ga" usually followed by adjective/adverb : Obasan ga kanashii desu (aunty is sad) Obasan ga heya ni imasu (aunty is in room) May this can help you :)

"ga" can be used for the subject of the sentence. "wa" can be use to point out the topic like: watashi wa (ha) "wa" can be also used only by women to express admiration. It is always placed at the end of the sentence. Check this page for reference: http://www.japan-activator.com/japanese-grammar/japanese-particles Hope it helps!

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