Is there a charge to download my music from iCloud?

I bought an iPhone 6. When I connected it to my new desktop, I got an error message that there was too much music to store on my phone, so it stored my music in the cloud. When I am away from home and I want to listen to my music, I have to download it from iCloud to my phone to listen. Do I get charged for these downloads? If I download a song once, does doing so prevent me from ever having to download that song from my cloud again?