How do I download ringtones to my cell phone?

I have a Samsung and I am with Alltel. I was told to go to a certain website and the ringtones are free. On the site it says they are free except what your carrier charges for downloading things off the net. Does anyone know what Alltel charges for downloading? Plus it says to save to my ringtones - how exactly do I tell something to save to ringtones? I consider myself pretty computer literate and I know how to use most of the features on my phone but this is just completely going over my head. So if any one has step by step instructions I sure would appreciate it. Thank you.