Data folder is the default place to store databases. Just accept the defaults and click next here.
You only need 1st one - 'Notes client' if you dont plan to make any changes to the code of the Gitabase Editor. If you want to be able to change something select 'Domino Designer'
Please UNtick the 'I want to connect to a Domino server' option as there is no server available and Gitabase Editor is just a local NSF database file.
Please make sure you DONT select anything on this screen.
As far as I can remember this should be it. After setup finishes, you should be able to open any NSF database file (with public access) in the Lotus Notes client.
If it requests anything else, just tell it "No" all the time.