Installtion problems

Having a lot of trouble registering. I registered on WP.com not knowing that it didn’t support customize theme sites. So kept trying to find the Install Theme button. =(

Questions:
Am I correct that a custom theme site must be registered on wp.org?

Does the SQL DBase name and/or the User Name and Password on my URL need to match exactly the User Name/Database on WP.org. ?

This has been a bit of a learning curve. Thanks for your help. Jo