VK Apps Hello World?

Question

PHP

I'm trying to understand what it is and what it is eaten with.
Can you give an example code for a VK Apps application that simply displays Hello World on a smartphone, and not a white screen? I just can not figure out how to make it work on a smartphone. Preferably without npm and npx.
It's even better if you output Hello, %username%. But I can already think of this myself, I hope, if at least Hello World succeeds.