How do players at low ratings actually manage to learn a couple of openings and then play them in games? I know the opening four or five moves to a couple of openings, but no sooner do I play the second or third move, the opponent doesn't play ball and play the regular moves that you might see of a higher rated player against those openings. They'll make moves that you never see in the lessons or tutorials in response to your opening. How should a low rated player deal with that?
I suggest you first study general opening principles with many examples. Then learn the first 5-10 moves of your openings suggested in the books.
If your opponent goes off the lines, then you can start to use the opening principles. Example: Control the center, develop quickly, castle.
I feel like experienced players may have trouble understanding this question... you probably don't remember a time when your thought process wasn't very efficient.
But do you have any tips for people who play too slowly? After I'm in time pressure I can speed up (I can play bullet and blitz). But when I have an hour on my clock I might take 2 or 3 minutes on every move until I'm under 10 minutes.
I suggest you to setup goals how much time you want to still have at move 10, move 20, move 30 and move 40. If you concentrte on smaller time frame it may help to keep your goal. If you play a long theoretical line for 10-20 moves then you need to adjust your goals for that, move time milestones forward from the point where you need to start to think in the opening.