A driver for the Defender Optimum MS-125 Nano mouse is not needed, but you need to match the device with the receiver. The desired combination of keys, the duration of holding them pressed, the sequence and similar actions are described in the instructions (0.09MB). In currently produced mice of this model, the word Nano may not be in the title.
For personal settings, use the Defender Mouser software (11.3 MB), and the manual for the Defender GameCenter software (4.1MB) will help you figure out how to configure . All instructions are in English in doc format.
There is also a manual (0.1 MB) for this mouse model in pdf format.