How to create a user in SQL Server Express database

Create a SQL Authenticated login first with CREATE LOGIN,

then add a user associated with that login to your database by using CREATE USER.

USE [master]
GO
CREATE LOGIN [YourUsername] WITH PASSWORD=N'YourPassword',
                 DEFAULT_DATABASE=[YourDB], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF
GO
USE [YourDB]
GO
CREATE USER [YourUsername] FOR LOGIN [YourUsername] WITH DEFAULT_SCHEMA=[dbo]
GO

from: http://stackoverflow.com/questions/3737449/how-can-i-create-a-user-in-sql-server-express-database-i-added-to-my-project

Then you would need grant permissions to this user, like:

grant select on [TheTableName] to [YourUsername]

Some SQL Server tools you can try: https://www.withdata.com/sql-server/