Here goes : when you click on "post reply" you should see the screen where you type a message. Above the where you type there is a smiley face and paperclip. click on the paperclip and a screen should pop-up so you can upload pics. If you have a pop-up blocker, you may have to turn it off so this screen can pop up. Then click browse, and find where you store your pics like, "My Pictures" folder. Double click the pic you want and then click the "upload" button. Should take a few seconds then close that screen out and click on the paperclip again and choose the pic you want to insert.
That is the best way my dumbass can explain it! LOL! hope it helps.