On this forum are tutorials. What you want to find are tutorials with names like state machine, doing many things at once and so on, I think there are at least 3 tutorials maybe more.
Basically NO delays, the main loop code runs continuously at full speed (millions of instructions per second) and you set variables from external sources that make the main loop take a side branch.
Here are a few https://forum.arduino.cc/t/flashing-multiple-leds-at-the-same-time/1065564/11
This may even be better
https://forum.arduino.cc/t/a-demo-code-explaining-the-switch-case-state-machine-and-how-to-do-things-almost-in-parallel/888172
Also, the IDE samples have BlinkWithoutDelay and StateChangeDetection. These are smaller, so they are more readily digested. Don't be surprised it takes months to get a good grasp, when I was training IBM programmers, they spent 2 years of 50 weeks x 40 hours before they were called an associate programmer. With Arduino, the libraries give you millions of debugged (mostly) code for free to use, so that two years is cut down by many months.