The attached script file is an SQL query that will shrink the database.
Users don't need to be out of the database to run this query but it may lock resources on the server for a short period (less than 5 seconds) depending upon the size of the log file and the database.
Unzip the sql file contained in the zip file to a known location. Either double click on the SQL file or open SQL server management studio and manually load the SQL file by using file --> open.
Execute the file by clicking the execute button on the toolbar.
Microsoft also supply instructions on Shrinking a Database - SQL Server here