You need to decide which of three different licensing schemes you want to use for it:
- Processor License: This is the simplest option. It is also the most expensive. You pay a flat rate for each CPU running SQL Server, and that's it ... and I mean CPU socket not per core.
- Server plus device CALs: CAL stands for Client Access License. Under this scheme, you pay one price for the computer running SQL Server (no matter how many CPUs it has) and a separate price for each device that accesses the data.
- Server plus user CALs: Almost the same, but in this case you pay for the server plus you purchase a CAL for each user that accesses the data.
Whether it's cheaper to go with processor licensing or CALs depends on how many users your application will have. If you're using SQL Server to back a Web application, you probably don't have any choice: unless you want to buy a CAL for every user or computer that hits your Web site, you need to purchase processor licenses.
On the other hand, for internal applications you may be better off with CALs if there are a limited number of devices or users that will access the SQL Server. Choose device CALs if you have multiple users sharing computers, or user CALs if you have users who roam among multiple computers.
Also, bear in mind that at a certain point it's cheaper to just buy processor licenses. For example, if you're running SQL Server Standard Edition on a single CPU, the cut-over point is around 25* users or devices; if you have more than that, it's cheaper to buy a processor license than to buy CALs. For SQL Server Enterprise Edition on 4 CPUs, the cut-over point is approx 400* users or devices.
*The number really does depend on what pricing you can get so you will have to do the maths
Please see the Licensing FAQ for details ....
https://www.microsoft.com/sqlserver/2008/en/us/licensing-faq.aspx
It's not hard to get your head around really .... I've also discovered that if you have allot of servers to license contact Microsoft because they can make things simplier still ... even introduce you the world of 'True-Ups!' ... now that's another story 