To give it your all is to hold nothing back in your effort. Go out there and give it your all.
It is encouragement said before the event rather than a description afterwards. It concerns effort rather than result, which is what makes it a kind thing to say.
1phrasegive it your allTo hold nothing back in your effort.
“Whatever happens, give it your all for the first half.”
give it your all is a phrase.
Practised in Idioms