Is Stronghold Europe free?

Yes. Stronghold Europe is released under Free fan mod (see the ModDB page for terms) and costs nothing. Neither it nor Stronghold Crusader HD has any paid content.

What do I need to run Stronghold Europe?

Stronghold Crusader HD, which is itself free. Stronghold Europe is an add-on and will not run standalone.

How do I install Stronghold Europe?

The PlayBound Launcher installs it in one click from Stronghold Crusader HD's mods list. You can also install it by hand — full steps are on this page.