Hey! Welcome to the site by the way
. Ok, to get the higher octave will be a little tough at first but you'll get the hang of it. When playing notes above the staff, you have to tighten your embouchure, which means pulling the corners of your mouth out more, sort of like you're smiling and make the hole between your lips smaller. The higher the note, the tighter the embouchure. DO NOT BLOW HARDER!!
That is a big no for playing flute. You will sound extremely airy and might even squeak. It doesn't take very long to learn, just practice in front of a mirror and see how your lips are placed and how tight your embouchure is. practice more on the lower octave and as you practice, practice going from the lower notes to the higher notes chromatically and each time try to go higher. As for the low C, I don't suggest working on those really low notes until the higher register is learned. That is what most beginner books suggest. I'm sure I know what you mean by that question and yes, you do press down the roller for that note. Good luck with learning flute.
I've been playing flute for 7 years and I was, still am constantly, getting the tighter embouchure advice drilled in my head. I hope this helped you!!