"wa" or "ga"

"wa" or " ga" makes a noun a subjective word by being attached in a sentense.

But ,we, Japanese, use them properly case by case.

Then , what is the difference between "wa" and "ga".

One thing Ican say is that "ga" is used in the case where something is specified or emphasized.

For example,
A teacher found that window glass of classroom is broken, and he thought someone of students did it.
Then he asked the students "Who broke the window?" in front of all of the students.

A student stands up and say "I did."

In this case, "Watashi ga yarimashita." (I did) is right , because the speaker emphasizing who did it.

On the contrary, assuming that there is a man whose work is to break glass everyday,
, he would say " Watashi wa garasu o mainichi warimasu."( I break glass everyday)
In this case, he needs not to specify anything.

I think it is better for you to learn "wa" and "ga" by encountering as much as possible.