You read the all the tutorials you can find. If you still doesn't understand then read them again.
When you have started to understand the basics of the syntax then get a JassCraft or a similar program with built in function list and syntax checker and start to produce simple jass snippets.
Read other peoples work, read the more advanced tutorials until you understand them.
Produce more advanced jass codes, release them to the public so people can learn or correct your errors.
And don't be afraid to ask for help if you have a more specific question.
If you can, try to get JASSCraft. It's somewhere at www.wc3campaigns.com and it's an awesome tool for JASS. Also, if you don't know the GUI, I suggest you start learning that for some experience with programming (although a different kind of "programming"), and so that you are familiar with how warcraft works. Just keep reading tutorials, and you'll probably learn a new thing each time, until you understand how the structure of how it works. This is how I learned.
I think we need to add something to the bottom of the front page that shows the Headline News forum that has a link to go to the News Forum Index so people can see there is more news. Do you guys see what I am saying, lets say you read all the articles on the front page and you get to the end and it just ends, no kind of link for MOAR!
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.