"dfx canister --network ic call" on another computer

I can request the “greet” function using the command in terminal “dfx canister --network ic call hello greet everyone” if canister was created my friend on another computer?

I have a backend from which I want to make some requests directly in the Canister function

If the canister was created by someone else, you need to ask your friend for the principal (canister id) of the canister and use that in the command line in place of hello.