Don’t worry, you’re not alone. I had a hard time finding it too before :)).
But anyway, all you have to do is click the “Customize” button at the sidebar right here —————————->
Then Click the “Community” Tab above your profile.
There you will see these:
Let People Ask Questions
Let People Submit Posts
Just check on whichever feature you want to enable, edit the title and other thingamagies, then click the “Save + Close” Tab at the upper right corner.
There you go. :))