you can attatch them as objects or you upload them onto an imagesharing site from where you get the url of the image and then type in
A lot of the times the imagesharing sites already show you the location with the IMG, then just copy and paste it here.
To fix your typo, it should be
[img]<Insert URL Here>[/img]
Or just paste the URL to the image in here, highlight it, and click the button in the normal reply page that looks like an image in a picture frame, and it will add the tags for you.