Type in the modpack name (Rexxit: Jurassic Pack) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select Rexxit: Jurassic Pack from the list on the left. The launcher will handle everything else!
I take a walk to down memory lane as I say goodbye to one of our longest running elements of our legacy infrastructure as we out with the old and in with the new. Its a good read, http://go.endr.me/oldbox1 enjoy!