You can't just add them from your computer or phone into a post here. They have to be hosted somewhere online first. Your home page here on the Hangout has photo hosting you can use. Uploads some images - the more the better - back, front, fingerboard/neck, peghead. Let us know when they're on your homepage - or you can use the richtext function to paste them into your message body.
It's not the easiest thing to figure out here. Steps:
Go to your home page (click on your name after you log in)
Scroll down and look for "Media" under "Activity" Click it
Scroll down and the third box should say "Newest Photos" There should be a green button that says "add photos" Click it
Click the blue button that says "upload photos"
Below upload photos, you'll see buttons that say "choose file" CLick that and navigate to where each photo is. You can upload 5 at a time.
When done, click the upload photos button.
This puts the photos in the system. Now go back to the thread where you posted your question and hit reply
You have to say something in the dialog box. Then, scroll down and you should see "Attachments" Click the button that says "photo" Then go to the pictures and click on each one.
Choose preview to see the post
When correct, hit "post reply"
As noted above, take pictures like the one in the ad you see. If it is a mystery model, people can help you if they see front and back pictures of the pot (with resonator (or back) off if it has one), the peghead and the neck. Usually once they see the peghead and the hardware, folks here are going to be able to tell you where it's from and who made it, even if not a common brand.