I have a Yamaha YPT-220 and Cubase 7.5. I would like to be able to set up a configuration that would allow me to press keys on my keyboard and have it play through Cubase, using the selected instrument track program. (Being able to input notes [record MIDI, basically] would be great too.) How can I achieve this?
Asian Squirrel, you can either buy a MIDI to USB cable, which I would not recommend because of the latency. Latency is the delay between when you press a key and when it registers in your DAW as a midi note. If you're interested in the MIDI to USB cable, here's a link:
It's the cheapest option.
You can also buy an audio interface, which is what I would suggest. I seem to get less latency using an audio interface. I've had a wholly positive experience with the focusrite scarlett series:
If you opt for the audio interface, bear in mind that you will also need to procure a midi cable.