what's the syntax to run my program on codechef's input files.

what should I do to make my program take input from codeshef’s files.

Simply write your code for getting input as you do for your own compiler, inputs from chef’s files would be read automatically. Yes, do keep in mind the constraints put by chef on inputs. Define the data type accordingly.

First, go on the links below and check out the videos on how to Solve Your First Problem On CodeChef:
link 1: Getting started

link 2: FAQ

See if these videos help, if you still have any problem understanding, you can comment below, in the comment section and ask about any trouble(if any) you are facing in solving the problem on codechef.