Extract the files you've downloaded in your Eclipse installation
directory. Make sure when you unzip those files, that it matches the
structure of the eclipse/features and eclipse/plugins directories.
[Maybe it's easier to unzip the files first in a separate directory and
then copy their contents to the appropriate location in the Eclipse
installation directory.]
Note that some plugins require other plugins (e.g. UML2 depends on the
EMF plugin), so you'll have to download/install these too.