When should I use 「が」 instead of 「は」 here?

I have a question about the difference between 「は」 and 「が」 in Japanese.

For example:

私は学生です。
私が学生です。

I get that the first one just means “I am a student,” but when would you actually use the second one?

I’ve read some explanations, but I’m still not totally sure about the nuance or how it’s actually used in real conversations.