Connect this to MIDI keyboard (or other controller) and sound comes out. Polyphonic means that it can play different notes simultaneously. Virtual analogue means that the device aims to emulate analogue synths while being actually fully digital.

It's a MIDI[1] synthesiser. You need to attach it to an external keyboard or sequencer to get any sound out of it. Think of it as analogous to network attached computer - on its own and disconnected, it's not going to do anything.

You'd typically attach it to a computer running some sort of DAW (digital audio workstation) software. Or a hardware keyboard or sequencencer.

It's "virtual analog" - which means it's trying to give the feel or controls associated with analog synthesisers which produce sound using oscillators and filters (extremely simplified description) rather than samples for example.

[1] https://en.wikipedia.org/wiki/MIDI