No problem!
Sure thing!
When you reply, you should see under the reply box: "+ Attachments and other options"
Click on there, and you should get more options, such as attaching a file
I should warn you:When you attack a file, it gets removed after a while (not sure when exactly), so if there are any pictures you don't want to go missing, upload them somewhere else and then post a link to the picture, or show the image by using the [img ] tag.
Hope that helps!