There is melee, currently just butt strikes, but the framework is there.
World Editor, but I think full functionality is not yet "unlocked."
From what I see, Workbench is an IDE, like Unreal's Visual Studio. At full functionality, you should be able to create your own games with it.
Did you actually find a download link?
I clicked every single button on this page, tried submitting my email, but I'm still not seeing any download.
If you go to the "Early Access" link posted on that page, it actually says;
"If you want to download Workbench, check our Dev Hub."
...in the third last paragraph, but it just links back to the same page you linked.
In the "Docs" link on that page, their listed tools does not include the workbench (or much else); https://community.bistudio.com/wiki/Category:Arma_Reforger/Modding/Tools/Official_Tools