I don’t know how to use a and the.
Please tell me how to use!

See a translation

"Please teach me how to use them!"

search for example sentences here:
https://tatoeba.org/eng

Trying to explain what "the" and "a" are used for will be quite difficult until you have a feel for what they mean. But basically, "the" describes a definite object, that is, something you've previously talked about or it's obvious to both you and the person you're talking which object you're talking about.

You use "a" when it doesn't matter which exact object you're talking about from a set of objects, but you just need one.

For example:
- "I'm going to THE shopping mall?" (speaker thinks it's obvious WHICH shopping mall)
- "which one?" (the listener is confused and doesn't know about this shopping mall)
- "Oh, it's just A shopping mall near my house" (It's not that important, it's just one of many different shopping malls around)

Hope that helps a bit...