Hello. I'm a student . I'm learning english for education.

"a" is an article to be specific about what you are

I know english- to an A2 level.

English does not have a type of level called A2. Since it is a grade to measure your progress, use related grammar like "to" to show the extent of your knowledge.
Use "an" as an article to specify your language level.

But, I don't know how to learning. I'm 22 years old.

"learning" is a verb in the continuous tense to describe ongoing action
"to learn" is in the root word that describes the action