I am not sure if this changes with whatever platform you are using, but at the very bottom of the post/editing page, there should be Add Photos and My Photos buttons. One takes you to photos in your gallery already, the other allows you to add to your gallery. Click or tap on the photo you want and it should appear on your post page. Does that help?
Click "Add Photos"
Click "Select"
Find and click on photo file on PC
Click on "Open"
Click on "Save"
As opposed to uploading photo's, how do you delete a photo from one's profile that you do not want. There does not appear to be a delete button.
