The Luff is how long the sail is from top to bottom. It thusly tells you how long to set your mast.
You have a 430cm mast. The luff is 434. So you set your extension to 4cm. Now your mast is 434cm long.
This extension (or base, but really it's an extension) is set to 20cm:
Boom is self explanatory; set it to 175cm.
Note that when you "downhaul" you pull the sail
all the way down to the bottom. Yes really. Keep pulling. No, it won't break. Make sure you are threading the rope correctly and for god's sake don't use anything sharp like a screwdriver to help you. I use the harness hook.
There are hundreds of videos like this on the web. I just picked a random one.