Meaning of “understand” - Learner’s Dictionary

understand

verb [ I, T ] us uk /ˌʌndəˈstænd/ past tense and past participle understood
His speech was very slow and difficult to understand.It was difficult to understand the logic behind his argument.I never learnt to understand written music.Use your dictionaries to look up any words you don't understand.Children don't always understand the difference between good and bad.
KNOW MEANING

A1 to know the meaning of something that someone says:

I don't understand half of what he says.
She didn't understand so I explained it again.
I understand written French but I don't speak it very well.
KNOW WHY/HOW

A2 to know why or how something happens or works:

[ + question word ] We still don't fully understand how the brain works.
KNOW FEELINGS

B1 to know how someone feels or why they behave in a particular way:

I don't understand James sometimes.
[ + question word ] I understand why she's so angry.
I/we understand (that)... formal

used to say that you believe something is true because someone has told you it is:

I understand that the school is due to close next year.
make yourself understood

to say something to someone in a way that they understand:

I had a little difficulty making myself understood.

(Definition of “understand” from the Cambridge Learner’s Dictionary © Cambridge University Press)