It's not real straightforward, I'm afraid. The photos must come from a hosting site. In the past I've used Facebook and Photobucket, but I've had problems with both. More recently, I've had success with tinypic. Once you put a photo there, copy/paste the url into the box that pops up under the photo icon at the top of your draft post. (From the right, it's the 7th one over.) Hopefully, that still works.
Good luck! I look forward to seeing your buddy.
Quaker Peppy (RIP my sweet pea), CAG Allie, dogs Wanda and Bonnie, feral kitties Cleo and Antoinette, mice Charlotte and Emily, née Jake and Elwood