I'm pretty new at this myself but I'll try me best.
1)Sequencers are what you would call "midi note/event" recorders. They function the same way as a conventional multi-track but instead of recording audio, they record midi data on the different tracks. This data is sent by a midi controller such as a midi keyboard / guitar. Once recorded, the data on the various tracks is then sent out by the sequencer via different midi-channels into a sound card/module, which then plays back this information using whichever sound patches you choose for the various channels.
Think of midi as electronic sheet music. All the info (notes, velocity, timing etc.) is there, all you need are the "electronic musicians" to read them and play them for you.
2)You would need a midi keyboard/guitar controller, and some sort of midi interface if you want to use an external sound module instead of your internal sound-card. How it works is like this: The midi-out of your controller connects to the midi-in of your PC's midi interface (This enables your midi controller to transmit notes to your software sequencer for recording). The midi-out of your interface is then sent to the midi-in of your Emu sound module (This allows your sequencer to send all the recorded midi information to your sound-module, so you can hear the notes being played back). You could then hear the sounds by connecting a pair of headphones to your Emu, or hooking up the outputs to a mixer.
3) I'm not an expert on this, but if you're just using it to sequence midi and not record digital audio, you don't need a really high-end PC. I will pass on this one though, anybody out there qualified enough to help?
