Dbav, you'll need an image host provider (such as Photobucket...which I use, and they have a free account available). Once you upload an image, or a gif file then you'll copy it to a post here on DI. The little icon to the right of the smiley face icon (image icon) above where you post...click that and it'll bring up a little box then you can paste your link from your image host account. That should do it.
Now you can use the media icon (to the right of the image icon) to link directly to YouTube videos, etc...without having to go through Photobucket, or whatever.
Hope that helps.
OFC