Why am I unable to fix the brake line on this '95 US truck?

I have a new master cylinder and a new brake line along with fresh brake fluid, but I still am unable to get any pressure?

What should I check or look at?

Ford F250

You have to bleed the air out of the system before you will have brakes. If you did not "bench bleed" that master cylinder before installing, it will take additional time to remove the trapped air.