Would anyone be so kind as to explain, in simple terms, what this type of synth does and why I would want to buy it.

cheers

Depending on your needs and budget, a microwave may not be the right choice for you - yet. If you're just starting out and want the maximum versatility for your money, you probably want to sink every penny you can find into the best sampler you can afford. Samplers just can't be beat when you need a 'jack of all trades'.

Once you've got the basic sounds covered with a sampler in your setup, you'll want to graduate to buying synths that specialize in doing certain types of sounds really well.
(There is no 1 box that does everything really well.) Which specialist synths you should buy depends on what music you want to make. The microwave is pretty flexible in it's sonic character, which is good. Provided you're not looking for realistic instrument sounds, you'd be hard to go wrong with the XT. It's definitely good for any kind of electronic music. A sampler (say a yamaha A3000 or Akai S5000) and an XT would give you a great little setup for writing dance tracks, for example. You'd just need a mixer, fx and some compressors, and you could make very high quality electronic music.

But really there's no substitution for listening to one at a store. I was sold after playing with one in Sam Ash in New York, and you'll either love it or hate it. But I'll bet on the former.