Windows Server 2016 License and Support

Hi,

I am new to Microsoft licensing. Hence looking for resources related to Windows Server 2016 and SQL Server 2016 Licensing. 

we have,

Windows Server standard core single MVL license

Windows Server CAL 2016 Single MVL license, and

SQL Server 2016 Single MVL license

We did not buy annual support on these licenses. My questions are:

1. Can we still use them?
2. What is the benefit of buying annual support?
3. What is the drawback if we use these licenses without annual support?
4. Can we buy annual support from 2023 onwards?

Thanks