As you rotate the engine the next cylinder to fire will be on its compression stroke. So, as you approach the 6-12 position the #1 piston is coming up in the cylinder, both intake and exhaust valves are closed, and the fuel/air mixture is being compressed so you will feel air being forced out of the spark plug hole.
The firing order is 1-8-4-3-6-5-7-2 (on the GM engines I am familiar with)
On one revolution of the cam sprocket, each of these pistons reach TDC, in turn, every 45 degrees of rotation. So at 45 degrees you would feel air being pushed out of the #8 spark plug hole, etc. -- at 180 degrees, the #6 sparkplug hole.
And of course that is why it is important to have the spark plug wires going to the correct spark plug in the right order.