Follow below steps to create a database user using SQL Server Management Studio.
1) Open SQL Server Management Studio and open "Object Explorer" and expand "Databases" folder.
2) Select and expand the database in which to create the new database user.
3) Select and expand "Security" menu. Right-click the "Login" folder, click to "New Login...".
4) It will open "Database user - new" window navigate to "General" tab from the left.
5) Provide "User name" and "Login name" in boxes provided.
6) Click "OK" button to finish the wizard.