When do you know when too use either in a sentence?
Maybe I don't get your question...but:
"has" is the 3. person singular while "have" is used for all other persons. So if the subject of the sentence is 3. person singular you use "has" otherwise "have".
He has a nice daughter. (subject: he 3. person sing.)
They have a nice daughter. (subject: they 3. person pl.)