Basically, you upload your pictures to a site that hosts them, Photobucket was mentioned, but there are also others. Some have different capabilities that you might see yourself using for other reasons than just posting here, so ask your friends.
Once you upload pictures, you need to learn how to find the "location" in which the individual picture is held. (Where to see it varies a bit with the different hosting sites) It takes the form of a URL with the http:\ and all that. You would highlight and copy the location with a series of mouse clicks.
Then, once you are in the AGF and composing a post, look for the little icon at the top, sort of to the right, that looks like a picture of a mountain with a yellow sky... must have been just after an atomic war.... That's the entry way to posting a picture. Click on that and it will give you a window asking that you put in a few words to be the link to your picture and in another space it will ask that you paste the location of the picture, which you copied from the hosting site.
Click OK and the picture should appear in your post.
Don't worry, it takes MUCH longer to explain than it takes to do it.
BTW - If you happen to choose Photobucket, the location of the full sized picture will be to the right of the picture, but it's the 2nd one in the list.
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