You have a range of input possibilities with the Focusrite.
There are four combo inputs on the front, so you can plug in four mikes. The first two inputs can also act as instrument inputs, so you can plug in a guitar. The second two are line inputs, so you can plug in, say, a synth. On the back are four additional line inputs which you can use for anything that has a line level output, e.g. a CD payer, more synths, or line ouptuts from a separate mixer.
All of these inputs are sent via USB to the computer, and in your DAW you can record all inputs on separare tracks, and yes, hear them when recording.,