It took me awhile to figure this out as well. I'll tell you what I do, and hopefully it will help.
First, you start a new post by clicking on + Post New Thread.
You'll get to a screen that lets you type in your message. Keep looking down, into the next section called Additional Options, and you'll see Manage Attachments in a blue box. Click on that.
A new screen pops up. First is upload files from your computer. Click on Choose File. That should show you your computer, and you have to find where you have the photos stored. I find it's easiest to have the photos on your desktop, but you might have them stored in a folder specifically for pictures. Once you find the photo, click on it to choose it. Then, click the blue box that says Upload. It may take a minute, and it may tell you your file isn't the right kind, if it isn't. There's a list of file types you can use at the bottom of that screen. If you have uploaded it sucessfully, it will show under Current Attachments. When you see it there, close the window.
Back on the other screen, where you can type your message, under Manage Attachments you should see your photo listed. Once you've typed your message, you can click Submit New Thread. And you are done!
If you want to upload more than one picture, after you upload the first one, while you are still in that same window, click on Choose File again and upload another one. All photos uploaded will show up in that post.
If this doesn't work, let me know, and we'll figure it out. We want to see your pictures!