In reply to ericinbristol:
OK. Let's just list the main skills required in belaying on a conventional (trad) rock climb:
1. How to belay the leader using a modern belay device.
2. How to belay the leader without a modern belay device (very important to know in the very serious situation in which the belaying device has been dropped and you have no other abseil device etc that you can use)
3. How to belay in sense of attach yourself to the rock/mountain when you've got to your belay ledge. i.e how to construct a belay. Vast subject.
4. How to arrange yourself correctly in relation to you belay/anchors.
5. How to tend to the 'dead' rope when belaying, to avoid it getting caught up around spikes /overhangs etc. below the belay ledge. Very tricky when the belay ledge is very small.
6. How to communicate with the leader, while you're belaying, if/once he/she’s out of sight.
7. The correct sequence/ procedure of dismantling a belay once the leader has arrived at the next stance.
8. The correct procedure for swapping over belays at a stance (i.e. when second has joined leader), depending on whether the leader is leading on, or if you're doing alternate leads.
The article you refer to above covers part of 1, not very well.