You just need them on your laptop. Then when you start or reply to a post (use Go Advanced not Quick Reply).
To attach the pic click on Image uploader
Browse and find the file on your computer
Upload
Realise file is to big, resize on laptop (I use PhotoFiltre)
Browse / Upload again, new file appears at the top of the list, click code to add to post
Your post will look like this with tags instead of photos
Click Preview Post to see the pics in the post
Once your happy with it Submit Reply