Not being funny Cliff, do you know how to upload a picture?
If you can then you're half way there, it needs to be hosted externally on for instance photobucket, imgur; I wouldn't use a cloud account though.
Assuming you know how to do the above - when you post a reply, there is a icon button you click to insert an image into your post, you then just type or paste the link to the picture.
If this makes no sense at all, no worries, just need a strating point - even newmarket can do it so you'll be fine