SQL Server security basic commands

Creating SQL Login for the users registered in Local Users / Groups (Windows ):

USE [master]
GO
CREATE LOGIN [SQL\snreddy] FROM WINDOWS 
WITH DEFAULT_DATABASE=[master], 
DEFAULT_LANGUAGE=[us_english]

Create SQL login :

USE [master]
GO
CREATE LOGIN [snreddy] WITH PASSWORD=N'lDÇ°ü†ÉUÛ^¼h nðÿ$©9 ke—z£˜ Ã`øM', DEFAULT_DATABASE=[master], 
DEFAULT_LANGUAGE=[us_english],
CHECK_EXPIRATION=OFF, 
CHECK_POLICY=ON

Creating user and mapping to Login :

Create user <User Name > for Login <Login_Name>  -- For SQL Login

Create user <User Name > from login <Login_Name>  -- For Windows Login

Note : 

Login will be created at server level where as user will be created at database level i.e

Login grants a principal entry into the server where as user grants a login entry into a database.

One Login can be associated with many users (one per database ).