It is easy to create a read only user in MS SQL Server Management Studio. When you create your user, simply assign the following roles:

• db_datareader
• public

Here are the steps.

1. From MS SQL Server Management Studio, connect to your database.
2. Navigate to Security > Logins and then right-click on it to create new user.
   
3. On the General page, fill all the required fields.
   
4. On the User Mapping page, assign your new user to a database. Then, check db_datareader role.
   

Test read-only user

Execute the following UPDATE statement.

-- Adapt the statement according to your case.
UPDATE TABLENAME SET COLUMNNAME=XX WHERE ID=XX;

It should return the following error message:

The UPDATE permission was denied on the object 'TABLENAME', database 'DATABASENAME', schema 'dbo'.