Update column values with column of another Table in SQL Server

Use update query with sub query.

CREATE TABLE [User]
(
    [ID] [int]  NOT NULL,
    [FirstName] [nvarchar](500) NULL,
)
GO
CREATE TABLE [usertbl]
(
    [UserID] [int],
    [Name] [varchar](50),
    [Template] [int],
    [Face Num] [int],
    [Access Group] [varchar](50),
    [Security] [varchar](30)
)
GO
INSERT INTO [User]
           ([ID]
           ,[FirstName])   
     VALUES
           (1,'John')
          ,(5,'peter')
          ,(6,'John')
          ,(7,'NULL')
GO
INSERT INTO [usertbl]
           ([UserID]
           ,[Name]
           ,[Template]
           ,[Face Num]
           ,[Access Group]
           ,[Security])
     VALUES
           (2 , 'Null' ,1,0,'Full acces', 'default'),
           (1 , 'Null' ,1,0,'Full acces', 'default'),
           (5 , 'Null' ,1,0,'Full acces', 'default'),
           (6 , 'Null' ,1,0,'Full acces', 'default'),
           (7 , 'Null' ,1,0,'Full acces', 'default')
GO

UPDATE [usertbl] SET [Name] = (SELECT [FirstName] FROM [User] WHERE [User].[ID] = [usertbl].UserID)

SELECT * FROM [usertbl]