At all

at all with a negative
We often use at all to emphasise a negative idea.
I didn't understand anything at all. (I didn't understand even a little)
She was hardly frightened at all.

questions, etc
At all can also be used in questions, and with 'non-assertive' words like if, hardly, ever and any.
Do you play poker at all? (=... even a little?)
He'll come before supper if he comes at all.
I hardly know her at all.
You can come whenever you like - any time at all.

'Not at all'
The expression Not at all is used (especially in British English) as a rather formal answer to Thank you.