14,494 questions
This is a very popular question and has been answered many times here and on other sites. Rather than repeating the same answers, here's some links.
https://www.microsoft.com/en-us/licensing/product-licensing/client-access-license
https://www.trustedtechteam.com/pages/microsoft-sql-cal-guide
https://softtrader.eu/sql-server-licensing-and-cals-explained/
https://www.mirazon.com/microsoft-user-cals-vs-device-cals-which-should-i-buy/