Enterprise Licenses

Hi Team

I have a Query for Licensing Part:

We don't have any Windows license. But we have planned to purchase the Windows license now. But we are using our OEM license only. I have an inquiry about purchasing the license. They have mentioned the base license. But we don't have a base license. 

My question is: Do I need to purchase the base license?  

Now i have downloaded the Enterprise OS and installed one test machine with win 11 Enterprise Evaluation. Is this possible to use OEM license for Windows 11 Enterprise?