Can someone tell me how to post a photo from a jpg file on my harddrive?

First you need to find someone to "host" (put it onto their web server) www.hunt101.com is one such place, there's others.
Second you need to "upload" it from your computer to their server.
Third you need to copy the URL (web address) of your picture (saving it to a folder named "pictures" in your "favorates" is a easy way to keep track of them).
Fourth, select the "Display Image-UBB Code" button above your post and paste the URL into the drop window.

Thanks!!