Go below the message window and click "Manage attachments". Have your camera plugged into the computer through the usb port and browse to the picture you want to upload. pretty simple actually, once you do it the first time.
Go to www.photobucket.comand "Sign Up" to create an account. Click "Upload Now", then browse to the photos you want to save on photobucket.
(I find it easier to first put your photos in one place, or make copies of them and put them in one place, like a folder on your desktop. It makes them easier to navigate to when selecting them in photobucket.)
(Also, you can upload several/many photos at once by using your CTL and SHIFT keys)
Once you get the "Upload Complete!" message (photobucket's annoying ad/music will likely be playing - hit the litte "x" in the top right hand corner of their ad to silence it), be sure to hit the "Save and continue to my album" link. You have to hit that link to "save" your upload. This will bring you to your "album", where you will see small version of all your photos.
(You can now spend/waste a lot of time organizing/editing photos, but you don't need to for Barn purposes. Just get them them in one album and saved)
Open up another tab or window in your web broswer, go to the Barn, and begin creating a post.
When you get to the spot in oyour post that you want to insert a pic, go to your other window/tab that has Photobucket open, put your mouse over a small picture (this will cause a menu bar and option list to open right below the photo) and left click once in the box labeled "img code". This will "copy" the big version of that image onto your clipboard. If you do it correctly, the code in that box will briefly change to "copied" as soon as you click on it.
Go back to your Barn post, right click and hit "Paste", and the code for your image will be inserted.
Once you preview your post or submit the post, the code will be then be seen as the actual pic you are trying to dispay.