When my friend installed the Essentials plugin, I and others couldn't do anything on the server, including placing blocks, destroying them, eating, etc. So I don't really know what to do.
But everything is fine when my friends give OP to everyone else, and it's working as normal.

Sounds like you installed EssentialsX Anti Build. If you aren't going to configure it, it prevents you from doing anything on the server by default (as the name might imply). Fix it or uninstall that plugin if you don't need it.

But how do I configure it?

plugins/Essentials/config.yml. Near the bottom, it's commented to help you

Sounds like you installed EssentialsX Anti Build. If you aren't going to configure it, it prevents you from doing anything on the server by default (as the name might imply). Fix it or uninstall that plugin if you don't need it.

Sounds like you installed EssentialsX Anti Build. If you aren't going to configure it, it prevents you from doing anything on the server by default (as the name might imply). Fix it or uninstall that plugin if you don't need it.

But how do I configure it?

Remove the Essentials Anti Build.