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.
Looks like Google fixed whatever mistake that made the recipes on the site go crazy and we are no longer trending towards a recipe site lol - I don't care though because it motivated me to spend alot of time on the site improving it and at least now the content people are looking at is not stupid and embarrassing like it was when I first got back into this like 5 years ago.
They also were digging threw old shit at the sheriff's office and I tried to get them to give me the old electronic stuff, but they said no. They can't give it to people because they might use it to impersonate a cop or break into their network or some shit? idk but it was a shame to see them take a whole bunch of radios and shit to get shredded and landfilled
Signatures can be edit in your account profile. As for the old stuffs, I'm thinking it's because Blizzard is now under Microsoft, and because of Microsoft Xbox going the way it is, it's dreadful.
@tom_mai78101 I must be blind. If I go on my profile I don't see any area to edit the signature; If I go to account details (settings) I don't see any signature area either.
You can get there if you click the bell icon (alerts) and choose preferences from the bottom, signature will be in the menu on the left there https://www.thehelper.net/account/preferences