how do you make a new face by selecting vertices ?

[wing_it_d3]

say we have two cubes and you want to create a face between the top of them I have tried selecting the top (two) vertices of both cubes no go, tried selecting the top (two) edges of both cubes again no go.

Throw in a 3rd cube and say we want to create a face between them all.

The reason I ask is because sometimes good things happen by chance but they need to be tweaked (not a reference to the program function) and this is how I am trying to tweak them.

thanks.