How to set what's displayed in top navigation bar?

1. Hi, I'd like to decide myself whats displayed in navigation bar. How can I do it?

2. After translating words Activity and Members in language file, Community menu on nav bar doesnt link to the proper sites. After picking one of them it says "site couldnt been found". Can you help me with this please?

URL: http://strefagrupowicza.ghb.pl/

Thx