Conditional 1
"If I find somebody's wallet in the street, I will take it back to them."
a) "If you find somebody's wallet in the street, YOU will take it back to them."
b) "If you find somebody's wallet in the street, take it back to them."
In sentence a) you are just hoping that the finder will take the wallet back to its owner.
In sentence b) you are insisting on the finder taking it back to the owner.
Conditional 0
"If you find somebody's wallet in the street, YOU take it back to them."
The sentence above is similar to sentence b), but differs from it gramatically. In Conditional 0 you are supposed to use either a pronoun, a noun or any phrase that is the subject of that clause.
"If you find somebody's wallet in the street, YOU will take it back to them."
"If you find somebody's wallet in the street, take it back to them."
"If you find somebody's wallet in the street, YOU take it back to them."