Here is the download link for CRM 2016 -> https://www.microsoft.com/en-us/download/details.aspx?id=50372
You will be given 90 days from Microsoft on installation to try out, build, test, and mock up any scenarios that you like in the new CRM release. At about the 60 day range you will start getting notices that you are getting notices it is time to officially register the software.
If you have software assurance on your current on premise licensing then this makes a very easy transition into the full featured release of CRM.
Once you are ready to convert the licensing all that is required is that you register your licensing through the CRM deployment manager and you will be up and running.