Sometimes there is a need to post photos that don't really belong in the photo Gallery, say selling gear, or trying to here is the best way to do it...
When you make a post, there is a box above the 'Continue' button you can tick off that says something like "I want to preview my post and/or attach a file." Tick that box, then hit 'Continue.'
You will now have the option to browse for a file, and upload it along with the post. The post will have an extra note in the suject line that says attachment, and is clickable...
You can leave it at that, and make a note to "See attachment," or you can get fancy.
I like to open the attachemnt, then copy the URL of the pic. Then I go back and 'Edit' my post, and add the link in as an image.
Good Luck...