What is this team for?

Question

cmd/bat

Can you please tell me why and what does this set command do?
I have a start.cmd file, it has this code, let's say

if exist test\gg.php ( 
  set TEST_FILE = test\gg.php
)

What does set do and why specify TEST_FILE? It's a variable, right?

Answer 1

What does set do and why specify TEST_FILE? It's a variable, right?

Yes. set assigns an environment variable.
Why - this is a question for the author of the script.

Answer 2

The availability of the test \ gg.php file is checked and the TEST_FILE variable is
assigned