Is anyone currently learning Japanese?

[Rynn]

As far as I know Ga is used when describing the subject or when the subject is being introduced. Wa is the topic marker while Ga is the subject marker. For an example: I was eating my dinner while Tsutsui-san walked in. It would be: Watashi wa gohan o tabete iru aida Tsutsui-san ga kita. Ga in that sentence would put the emphasize on Tsutsui-san because he walked in.