Hi Jason,
Welcome to the NAV world! 
There are different steps to do this and when I’m describing here goes for the classic client (not three tier setup).
The easiest way is just to copy your current database, or use backup and create a restore into a new database.
In general it’s a very good idea to have a test database. In fact I always advise customers to have both a development, test and production as a minimum. This way you can do your changes in the development database. Then you can copy the changes only to the test database, and when you have approved the changes, then finally they are moved to your production database.