You can also learn a lot of the basics from Bubba's tutorials
. Though they're for Quake 3 specifically, JA and JO use the same engine and so a lot of the concepts are the same--it's just some of the particular entities that are different.
Also, check out the tutorial sections of Map-Review
when you get to some of the more advanced stuff. Save these links, you'll want to refer to them along every step of the way!
Some useful programs to get for editing:
, the actual map editing tool.
, a superior compiler.
, a graphical interface for q3map2 so you can compile maps easily before you know all the switches and syntax.
And always, always, search for answers on this or the JO mapping forum, and ask questions!