Easy. I helped dad do that throughout our house. He has done a hundred rooms like that.
Get a round LONG bristle brush.
Something like this:
You spread the mud on the ceiling rather thick.
Then "stomp" the pattern into it.
Follow the directions that QGM (above) linked to.
A few tips:
1 Get a LONG handle on the brush so you don't have to lift your arms over your head when stomping the ceiling.
2 You can you a premix like this:
Instead of adding water to the mix use a ceiling white PAINT.
It will dry a bright white.
3 It's a messy job so clean it up while it's still wet.