Then you select the part you want to make the ringtone out of. I recommend selecting a second or two before the start and after the end. Then copy it using Edit or control-C.
Goto File, New, then in the new window goto Edit and Paste.
Trim the file to what you want.
then when you have it how you want and what volume you want(dont go too loud else you get distortion. also watch out on heavy bass)
then you goto File, Export as Mp3
Make sure you fill out the IDv2 tag information. If you dont it is easy to lose what is what. I recommend naming it something like songnamechorus or songnamefirstverse so if you have multiple files off the same song you can tell which is which.
Then locate your file if you didnt save it somewhere special. It will be located here
Copy your ringtone to the SDcard for your phone using the USBcable to connect your phone to your computer. I created a Ringtone folder in the music folder for myself so I did not get them mixed up. You could also just make a folder named blah and place them in there. The key is to keep them seperate from your normal music else you accidently infect your playlist with silly ringtones.