How do I create a new database using the custom tables created by me in another database?

When you open the app or login to the website you will see your DBs, if you hover over the top right corner of the DB icon you will see a drop arrow. If you click on that you will see the option to duplicate your DB.

Ok. What if I want to copy a few tables from a testes into a production database?

testes = testbed 

Sadly there is no way to move tables between DBs.

1) You will have to manually recreate the tables

or

2) Duplicate an empty testbed DB and then import the data from production

:-(

Thanks for answering though, Fred.

If you are using the native application you can share the tables when importing.  This only works on the native app in Mac though.  

I am afraid I don't quite follow you Nick. What do you mean share when importing?

Ninox app for Mac, has a choice to import from another Ninox DB

OK, thanks I didn't realize. Is this in the Table -> Import Data menu?

Ok got it... It's in the top view of the database. Import Data. And then just choose. One must be in the db top view. Thanks Nick!

Looks like two Nick's involved in this one!  The other Nick needs the credit.  

Oh. Right! Thank you both for help!