You need somewhere to host them like www.photobucket.com and it's free and you get 2 GB of space for photos and videos,once you have uploaded it to there you will see a url for the image below it right click on it so it's highlighted and click copy.
Then in your post click the image tab which is yellow and paste the image url into it and click ok and the image will appear when you click add reply.
Then in your post click the image tab which is yellow and paste the image url into it and click ok and the image will appear when you click add reply.