How do I get my songs off itunes on my desktop library onto my iphone4?

itunes was kind enough to reinstall my first 3 songs that downloaded and accidently deleted from my library when I did the first update. I can't seem to get them on my iphone4 now though. They are in my itunes library on my desktop computer but how do I get them back on to my iphone 4 which is were I purchased them. When I open itunes on my phone and touch "purchased" it goes to ipod and there it says "No Content" Any help would be really appreciated.
Thanks. Trish