the pics have to be "hosted on a server" somewhere... to do this, you "upload" them to a host, like photobucket or RS or several others...
once loaded to a host, the pics get assigned a url (uniform resource locator, also known as web address) once you get that address you put it in a post & pics appear
to get the url, once a pic is loaded to a host (which is free) right click & select Copy Image URL
then paste that into a post this image syntax around it
like this
once you do it once, it's very easy
if you happen to have an iphone there a free photobucket app for it, loads pics you tank in seconds , but you can load them to photobucket in less than a minute from your pc