How do I upload a script?
It's already straightforward: To post scripts your first have to sign in, then click "Publish a script you've written", which it's the very first link in your profile page.
Otherwise, just look on the help page (https://gf.zukizuki.org/en/help) and you will find "Development - How to write user scripts" guide, which of course includes a link to publish the script.
The main page is meant to guide the users in the process of understanding the purpose and installation of userscripts.
There is no link in the navigation menu anywehere to upload a script. This is a script sharing site. So uploading scripts and downloading them should be like, um, one of the most easiest tasks to do. It's sad that I have to actually GOOGLE "Greasy fork upload script" to find the actual link to do this. That needs fixed.