I have a picture on my computer that I want to use, but I know... I'm a total noob XD I have no idea how to put it in my rp post. Would someone be kind enough to tell me how to take a computer picture, not one from a url, and put it in a post? I'll give you a cookie?

You need to upload the photo onto a photo hosting site like Photobucket or OMGImages. Once you've uploaded, the site will give you a URL that you will be able to post or link to.