When you are writing a post, click the little picture image to the left of the smileys icon.
You will then be presented with two yellow boxes. Double click the "Browse you Device" box and you will then be able to double click an image from your computer.
It will load - then click the "Upload" box at the top right. In a couple of seconds you will see the image attached to your post.
Then click reply as normal. The whole process takes less than ten seconds.
Off you go.....