Okay, road bike experts. I know how to shift a three speed efficiently

, but the 14 speed 89 Panasonic is a new world.
So... dt shifters. Left one is the big gears, right one is the little gears. That's about all I know. I
think (and this is how stupid I am about this stuff) that if my chain is on the littlest big gear, and the biggest little gear, I'm in the lowest gear on my bike. Correct? Sheesh. I know NOTHING about this. Twenty-two years since I rode one of these, and I think I sucked at shifting then. I know one uses lower gears to climb, and bigger gears to go fast on flats and downhills, if one is so inclined. I know that when it gets too easy to pedal, I shift up. When it gets hard, I shift down. I bet there's more to it than that. What do I need to know to use my bike most efficiently, and to not look like an idiot?
Having seen
Breaking Away many times, I realize that I need to avoid racing angry and imperious Italians. Otherwise, I feel like a total newb.
And I have both indexed and friction shifting. I do not understand this, either. I know I'm in indexed mode now. So folks, educate me!