Here is a solution for you: http://bit.do/gmj4, which provides a tool dedicated to helping you transfer files, such as music, photos, etc. between your computer and Android phone, that is, iPubsoft Android Desktop Manager!
You can be able to download music from your computer to your phone using a USB cable. Once you have downloaded music from online websites and you have it on the computer, the process should be easy. You connect the phone to the computer using the USB cable and then select the songs that you would like to have on the phone. You can go to http://www.wikihow.com/Transfer-Data-Between-a-Cell-Phone-and-Computer for more details.