Hello. I'm not the best at this either, but if you have the picture stored on your computer, when you reply click on the "browse" thingy at the bottom of where you post and then put the location of the picture in there and a link will come up with the post when you finish your message.
If you have it on a free website like Imagestation, or another, then you type in before the address of the picture img with a [ ] around it and at the end of it, /img also closed with a [ ].
If you're using Image Station, you'll come up with the url for the photo with an extra ".orig.jpg". Delete all of that after the ".jpg" that preceeds the ".orig.jpg" or it won't post the picture.
Best.