there is no such thing as a stupid question here...
rest easy man..
HOWEVER...
there are questions that merit hilarious responses ...

Too bad your question did not merit such attention ...

Installing the repo ?
well...in a way...yes..I suppose one could call it that.
Rather what is done is putting the exact web address of the repository or repositories in question...into a specific "place" ..usually in maemo terms...
called a "repository catalog"
(I would imagine it isn't much different for Harmattan ...not having used it myself...but it is in the maemo family so I would imagine it follows the same ..)
Where once you have done so ...upon opening your available apps list to download programs..
Magically.. the newly added repo is accessed and there are suddenly programs available from the repository you just put into your repository catalog ...and enabled....

Hope that brief blurb demystifies things for you.

- I would suggest opening your app catalog and there you will see an option to add new repositories.
- Add the required link ..
- enable it.
- close the repo catalog.
- Let your app catalog update itself to include the new available apps..
- Go shopping for new apps
- Endsormeans' your uncle.