Moussaka Recipe

I expect some guests today and I want to prepare a delicious meal for them but I need some help. I have my grandma's moussaka recipe, it seems easy to do but it takes some time to put it together and I think a helping hand would be welcome. Could you give me a helping hand? There are some steps I need to follow in order to make this so complicated dish but I'm confident that with your help I can make it. Let's see...my grandmother's recipe says to start making the meat sauce, and while that is simmering, we should prep the potatoes and eggplant. There is also a note that says that we should make the béchamel sauce at last because it is not a sauce that holds very well. I'm so confused :( someone please help me!!!