Can you narrow the scope of the question - it is really way too broad. We can get you started with: You need a recorder! 🙂
This can be a certain Yamaha keyboard or a stand alone recording device. Yamaha happens to make many different types of recording devices.

You'll need a microphone... a device to take air molecules in motion and turn them into electrons.

Beyond that everything will depend on the device you choose to do the recording. Can you give us an idea of what you want to accomplish. For example, if you told us you owned a Yamaha Synth (since this is the name of the site) we could tell you how to proceed. You might need additional gear to add to that synthesizer in order to record vocals. But with no information I'm afraid, we cannot be too helpful.

You posted in the "Vintage Yamaha Synths" forum, which do you own?