The Microsoft mouse buttons have default assignments when you first use them. Some of these button commands may not work in the program that you are using. For example, the default button assignment for the right button is Right-click, but some programs may not support this command. Try pressing the button while you are using programs that you are sure support the button's command. You can also reassign the button to a different command.
The button may also be assigned to a command that you are not familiar with. You can find which commands are assigned to each button, open the Microsoft Mouse and Keyboard Center software, and locate your device.
Try reassigning the middle button to Middle-click.
For information about reassigning mouse buttons, see How do I configure basic settings for a Microsoft device?