Can't put songs on iphone

Perhaps you could give some detail. It is difficult to suggest anything with so little information.

You connect iphone to itunes? Itunes recognizes iphone?

Hoe do you try to sync?

You select sync music? You select the music you want?

You select manually manage?

You click sync? It syncs? Do you get an error message? What does it say?

If you want to manually manage music with your iPhone which provides no benefit over syncing music since an iPhone does not support disk mode as is supported with most iPods, you must select manually manage music and videos under the Summary tab for your iPhone sync preferences with iTunes.

http://manuals.info.apple.com/enUS/iPhone_UserGuide.pdf

Did you select sync music under the music tab (check the box)?

Did you check the box by the music that you wish to sync?

Did you click sync?