The most basic procedure for installing Papyrus consists in installing the Eclipse Modeling Package for your own platform.
Then, you have to use the discovery interface ("Help" => "Install Modeling Component") and select Papyrus.
Papyrus Update Sites
Eclipse provides facilities for adding new software to the platform or updating software in the system.
In all cases, the site location (i.e. the Web URL or the archived Update Site provided above) is the only required item to update or install a software within Eclipse.