Having trouble syncing

I downloaded the brand new itunes on my new laptop and now i am having trouble syncing new songs that i have downloaded onto my phone. When i click sync it doesn't sync them. I cant transfer my purchases either. I have about 400 songs on my iphone but 10 on my itunes library and i dont know how to transfer the songs over like i could in the old itunes. When i click on my device and go to the music tab to try and sync the music itself, it only gives me the erase and sync option, but i dont want to do that because i will lose the 400 songs that i have on my phone. What do i do? Please Help! 🙂