At your membership level you need to use a photo hosting site like Imgur.com. You create an account on the hosting site, upload your pictures into your account, then when you click on your picture you will see several codes that Imgur assigns to that picture, then you insert the BBCode into your post. I just write the code on a piece of paper and type it into my post here on the forum.
The other way to post pictures is to purchase a membership. That will allow you to post pictures directly from your computer by clicking the "Insert Image" icon in the top of the post box (the "Insert Image" icon is the little picture between the chain links and the smiley face).