Translate It is all described on wiki. Weblate is only a tool to simplify translation for language pack, but you still need some basic knowledge about git and Composer/Packagist to create and maintain such package. Unfortunately there is not step-by-step tutorial how to create new language pack, and Hebrew may be even trickier than rest of languages because of RTL. If you don't understand how it works, it may be better to find someone who will maintain Composer package and handle technical stuff, while you can focus only on translations through Weblate. There were some language packs for Hebrew in the past, you may try to contact with their authors and revive one of them: https://discuss.flarum.org/?q=hebrew
As last resort, if you only want to translate your forum, you may try Linguist: https://discuss.flarum.org/d/7026-linguist-customize-translations-with-ease
