Pastitsio is sometimes referred to as Greek Lasagne -- a name which I don't think really does it justice, since it is brilliant in it's own right and needs no comparison. It is kinda like lasagne though.
The basic steps are to make a meat sauce (this can be done a day or so in advance if you want), then you cook up some noodles, layer the noodles and meat sauce, coat the whole thing in a creamy bechamel, bake it up and delve into culinary heaven when it's ready! Huzzah!
Ok, now on to phase two: noodles, bechamel, assembly and baking. You can stop here and do the rest another day, just remember to heat the sauce again to make sure it will spread out easily when you go to assemble the casserole.
Καλή όρεξη! (Kalí óreksi!)