Japanese learners meet は and が early, but the difference becomes clearer if you think about information flow.
は marks the topic
Use は when you want to say what the sentence is about.
- 私は学生です。 — As for me, I am a student.
- 今日は暑いです。 — As for today, it is hot.
が marks the subject you are identifying
Use が when the subject is new, important, or the answer to an implied question.
- 誰が来ますか。 — Who is coming?
- 田中さんが来ます。 — Tanaka is coming.
Quick practice
If you can translate the feeling as “speaking of…”, try は. If you are pointing out “this one / this person”, try が.
Kanjiru blog posts can be expanded into short drills, example banks, and JLPT review sets later.