Explanation of Lookup function and vector form with table as a range

I would like someone to explain the Lookup function in a more dumbed down version than they have elsewhere.

Then explain the difference between the Vector Form and the array.

Then explain what the gmetrix Excel 2013 expert practice test is asking me and why the solution is what it is. Part of my confusion is that the vector range is a whole table, and the vector result is only one column. And I thought the two had to be the same size.

Thanks you.

Maybe take me step by step through it and see if I understand that part before moving on to the next.