When these sentences are used?

I thought this

I can’t understand it.

I can’t understand it.

When are sentences used that thought in Japanese school?

I amn’t knowing it.

I amn’t knowing it.

When are some sentences used at? example:”this is a pen.”.

I can’t understand it.

I can’t understand it.

When are sentences used that thought in Japanese school?

I amn’t knowing it.

I amn’t knowing it.

When are some sentences used at? example:”Lemon is sour.”.

These questions cant be understood forever, because nobody try use there sentences.

Is leaning these having any means?

I already understand it.

There sentences are useful to teach basic English.

But we need leaning more useful it in everyday talk.

I want to use English as a communication tool.