View variables in PHP code at server

I have a host server at a web-hosting and my PHP file is lodated in a folder at server. From my HTML form, I send some data and I like to view all those variables in my PHP code at server side.

All discussions said to use print, print_r or echo. I used them, but I don't see any output or frankly is no idea where to see those outputs. I checked in the console (F12), but nothing is there.

My query is I have PHP code in a .php file located in host sever, how can view variables in that PHP code?

Thanks