How do I Copy over music over from my laptop iTunes music library to my iPhone music library?

How do I Copy over music over from my laptop iTunes music library to my iPhone music library?

I know where my iTunes music library is on my laptop hard drive. I know how to fire up my iTunes app on my laptop and connect my iPhone via USB to my laptop. And I see that it shows up and can be selected.

I have the iTunes Store and Music apps on my iPhone 5S running iOS 8.4.

I somehow have an odd assortment of the music on my iTunes library on my phone, but it's nowhere near the collection I'd like to have there. There are even songs on my iPhone I'd like to delete without necessarily deleting them from my overall music collection.

How do you do these things??

I've really tried messing around but find no way to get either thing done.`

Help?

Steve