Welcome. It's about time you joined us officially...
First you need to upload your pics to an image hosting site (google photos, imageshack, etc..)
Then you copy the image url and paste it in the reply box. If you look at the reply box, you'll see a few tool boxes above where you type. It'll be the 2nd icon in the 5th box. It looks like a square with a green/white + on the bottom right. Click the icon/button and it'll open a little window. Paste the copied link in the top box that says URL: