Hi Chynna,
It is not a good idea to try and allow people to have access to your computer from the internet, particualrly these days with viruses, spyware etc - unless you are very techno savvy.
You need to copy your file to some site that specialises in 'hosting' as indicated above in the forum stream by Tim.
One 'free' way of doing this is to use the 'free' hosting site that many ISP providers give you. Here (in Australia) most ISPs give you a free 20MBs which is enough for a few MP3 files.
I have written a 'Getstarted' help document at one of my websites at:
http://www.getstartedhere.info/Web_Page.php which you may find explains in non-technical terms how you do all this.
Cheers ... Clyde