It may be worth noting that some websites will automatically convert anything in a post that "looks like a web address" to a link. You also may receive email where the sender just typed the URL, but your email program made it into a link. I'm not sure I agree that's always a good idea; but you do need to be aware of the "traditions" on any site where you may want to post.
(whb - ignore the following for now if it's confusing:)
IF I were posting here, on mudcat, a link to this thread from some other thread, I could shorten that to typing:
The "leading slash" would tell my browser that it's a local link on whatever site I'm on when I click it. The link would look the same, but the address it's using wouldn't work if it was posted anywhere except at mudcat.org.
If you use the complete web address, it will always (never say that) work, posted anywhere on the internet, or in some cases "posted" in a document on your own computer. Anything less than the complete address is only good for jumping around within a given server after you're there.