Generally speaking, that's gonna depend on "where your at" with using computers and drawing/layout. I use Visio, it's not my favorite, but it's good at whacking out a quick diagram.
It's pretty much drag & drop icons onto the virtual paper, then connect the dots. It does support layers, it has lots of features to help the non-proficient dress up the drawings.
All-in-all, I like it.
Good Luck
Scott