From what I understand SQL Server should only use the auto file growth option when it needs space, correct? I have a database that was created at 50GB size and is set to 10% auto grow. If I run a sp_spaceused it returns a size of 65GB with 39517GB free. The transaction log was set to 15GB. The acctual .mdf file is 51.2GB but it only backs up 11.1GB. So, here are my questions:

Is the 65GB size the 50GB .mdf and 15GB .ldf files added together?
When will the Database start to grow, once the unallocated space gets below 10%? If the unallocated space is 9% does it grow an additional 10% or just 1%.

I am new so please be kind

Thanks for your help

P.S. I did some searchs first but could not find this answer.