Basis in Switzerland

Hello Denita, welcome here! I can imagine you want to return to Switzerland after your short stay in Grindelwald :-). As for your questions:

1) Assuming that you want to return to the Grindelwald region (in the Bernese Oberland), centrally located towns would be Interlaken and Spiez along the shore of lake Thun. Interlaken gives good access to the Jungfrau region and has camping sites in and around the town, whereas Spiez also offers direct connections to Thun, Bern and Brig in the canton Wallis. Both towns are only 20 minutes apart by train, so there isn't a major difference in traveling times. You can plan your trips using the online timetable.

2) A visit to the Jungfraujoch is indeed an exciting and beautiful day trip. The same goes for the Schilthorn, which has spectacular views of the Bernese Alps. Other trips I'd recommend (again, assuming that you will mainly discover the Bernese Oberland) are boat trips on lake Thun and/or lake Brienz and a cog railway ride up to Schynige Platte or Brienzer Rothorn.

I hope your first forum experience turns out to be a good one!