here is a little more information on some different kinds of links:
a link WITH the http:// is called an “absolute link” while a link without the http (so, a link that references something internal to the site the document that doing the linking is on is called a “relative link”.
the thing that is different between the links is called a path:
http://www.somecoolsite.com/some/directory/index.html is a path, in this case an absolute one
these are all relative: (relative to where you are currently/what you are currently looking at)
/going/in/to/these/directories/and/loading/a/file.html is a very long path to a file in some nested directories
../../../../../index.html is a path
and so is
/
all are basically instructions on where to go and what to load.
you can consider absolute paths a bit like “drive to this completely new city, then to this address, then to this room in this building and talk to so-and-so”
wheras relative paths are: “stay in the same building you are currently in, go to the lobby, take the elevator up to the 5th floor, then find room 505 and talk to the person there”
both ultimately do the same thing but make different assumptions 