Don’t worry about being a “noob”, everyone’s got to start somewhere.
Ok, to post an image into a reply you need to have a hyperlink to the image and paste it into the Insert Image box (which is the last button at the top of the reply box, the one that looks like a clip art mountain). To get the hyperlink you either need to have the image hosted on another website or have it already hosted on here as an attachment. Then open the image in a new tab and copy that url.
Hope that helps.