When you plug in the USB receiver of Microsoft Arc mouse, Mac OS detects it automatically within a fraction of second. That means, Microsoft Arc Mouse works out of the box without installing any driver for it. But, in order to get all the features, it is suggested to install the driver.
The required driver will be downloaded as shown on the above screenshot. After download is complete, Mac will prompt you to take next action. Accept the security prompt and software policy etc. and enter your password to install:
You need to configure your Microsoft Arc mouse from Application folder. It will show as Others with an pointer icon, double click it to get the settings window:
You can configure Arc mouse setting for individual application too.