I started learning 한국어. Some examples start with 저는 and others start with 제가.
How will I know if I should use 저는 or 제가.
저는 : when you try to describe yourself in general. More like a fact...
ex - 저는 사과를 먹었어요. (I ate the apple.)
저는 키가 작아요. (I am small.)
저는 그림을 잘 그려요. (I draw well)
제가: when you try to describe what you did or how you are to someone.
ex - 제가 그 사과를 먹었어요. (I ate that apple.)
제가 좀 작아요. (I'm a bit small.)
제가 그림을 잘 그려요. (I draw well.)
Hm.... now that I try to explain it's quite difficult... it's just natural for me to know when to use which, but to explain, it's harder. If anyone has a better explanation, please go ahead.
A teacher once explained it to me this way:
You use 가 for normal/usual things and 는 for unusual things/things that are out of the ordinary for the subject to do.
A Korean mom cooks Korean food (which is perfectly normal and nothing to be surprised about) -> 엄마가 한국 음식을 요리했어요.
A Western mom cooks Korean food (which is unusual, so I want to say "MY mom cooked KOREAN food!") -> 엄마는 한국 음식을 요리했어요.
No guarantees, that's just what I've been taught. :)
This also seems like a good explanation:
I think 이/가 and 은,는/을,를 is probably one of the harder grammar concepts for English speakers to understand because using one or the other has a very subtle difference.
Look for youtube videos that explain this (BillyGoKorean explains this well).
And since it looks like you are a beginner, my best suggestion is learn it as best as you can and accept that right now you will not know this 100%.
With time you will grasp this fully so don't drive yourself crazy trying the perfect this now.
Non-answer, I know.