If in doubt, read the plugin author's page:
"A touch friendly interface for Mobile and TFT touch modules"
In other words, it adds responsive CSS stylesheet'ing so that if you run the OctoPrint web interface locally on the Pi's TFT screen then everything will be smaller and more useful for a tiny screen. And yet, you'd still need to run a browser locally on the Pi to see the OctoPrint web interface.
This isn't a solution where there's a unique GUI application which runs locally on the Pi and which talks to the TFT screen. It's a browser-based solution for the Pi.
It does allow you to control the printer. Read the plugin author's page for details.
If in doubt, read that plugin author's page:
"OctoScreen , LCD touch interface for your Octoprint... that allows you to control your 3D Printer, like you can do with any LCD panel on the printer controller board itself, but using OctoPrint and a Raspberry Pi."
He further describes that this doesn't require a browser. He describes how this is different from the TouchUI plugin.
Honestly, if this is confusing then don't buy all the stuff. You're in the hacker space now where people who do this are expected to know a lot of things like how to make Linux happy, how to make electronics happy and how to load (compile) drivers sometimes.