When you edit the design of a mortar, the mortar widget will appear. On the right are several buttons: copy, paste, undo, ok, and cancel, from top to bottom. Currently, only Ok works. On the top is the mortar's title and the current stage you're editing. The other options are used to edit the current stage's behavior.
A firework is composed of 1 to 20 stages. Each stage is launched from a parent stage except for stage 1, which is launched from the mortar.
Additional design information: Pyrotechnics Examples, Pyrotechnics Bugs, Gardiner's Pyrotechnics simulator, RedStorm's PyroSim
For constructing the fireworks: Pyrotechnics Formulas, Public Pyro Labs, Pyrotechnics TechTree
For competing in the The Test of Pyrotechnics: Pyrotechnics Stadiums, Pyrotechnics Contests, Pyrotechnics Contest Schedule
More information can also be found by searching the archived forums or the new forums.
You should also consider joining the pyromainiacs forum www.atitd.info and one (or both) of the in game Pyromaniacs guilds (RP Pyromainiacs and 7L Pyromainiacs).
You'll need a mortar (15 Firebricks, ability learned at any University of Art & Music that has completed Pyrotechnic Mortar Construction), then when you click on the mortar you'll bring up 20 stages with the following options, which you can tune your firework with. Mortars are reusable; the design can always be changed and the mortar armed and fired. When experimenting it's best to set each of the glowers to 'NonGlowing' so that it doesn't cost glowers. The shells are easily visible.
Notes:
1) Egypt has a gravitational acceleration of -10.26 (approximately, results have varied slightly).
2) Using both thrust and rotation on the same stage might not work correctly. Specifically, using left/right rotation and thrust doesn't work. Using upward/downward rotation and thrust seems to work ok. For a little more information, see this post.
3) Left/Right rotation appears to work relative to the ground, not the current stage. For a rocket going straight up or down, left/right rotation will have no effect. Upward/Downward always seem to have an effect, though the direction might be opposite of what you expect.
5) If stage 1 is 10 seconds long, and stage 2 is a funnel from stage 1 that has 4 launch repetitions with 10 rockets, then 4 funnels of 10 rockets each are fired when stage 1 is 2.5, 5, 7.5, 10 seconds old. If the launch offset is set to 2, they are fired when the parent is 2, 4, 6, and 8 seconds old. This is different than what I'd thought before - appear incorrect to anyone?
If stage 1 is 10 seconds long, and stage 2 is a funnel from stage 1 that has 1 launch repetition with 10 rockets and a launch offset of 3 seconds, 1 funnel of 10 rockets is fired when stage 1 is 7 seconds old.
Each mortar has some presets that allow you to experiment with pre-designed display.
To arm a mortar you'll need some papyrus paper (papyrus growing guide: papyrus), Aluminum Powder, and gunpowder. To add color to your firework you'll need some glowers. Gunpowder and glowers are produced at a Pyrotechnics Laboratory. See Pyrotechnics Formulas for formulas. Once the mortar has been armed, it may be fired.
See also: Pyrotechnics Examples, Pyrotechnics Bugs, Gardiner's Pyrotechnics simulator, RedStorm's PyroSim, Pyrotechnics Formulas, Public Pyro Labs, Pyrotechnics TechTree, Pyrotechnics Stadiums, Pyrotechnics Contests