Hi there, ( thanks Stefanie )
you will need to import the Content if you want any layouts that are part of a page or a GP Element.
although sites from the library are only recommended for install on a new clean site, you can import them into existing sites with some care. To begin you should make a backup or use a staging site before making the import.
Alternatively you can always import the site to a development site and copy and paste the content you require to your other site.