When it comes to learning software development or coding, it’s always best to immerse yourself in as much practice as possible! Taking notes - especially on paper - is great for really imprinting the lessons in your memory.
However, there is no substitute for actually coding. It’s great when you sit down and try to apply what you learned. You’ll try taking in a string from the user, try to capitalize it, and realize you forgot exactly how. This forces you to look it up, apply it, and really commit it to memory. Sometimes, your most important learning is done when you try to do stuff on your own, fail, find the solution, and forge onwards.
As for conditional statements, you use them a lot in coding. Most the time, you need your code to be able to make decisions or account for certain situations. Say you write a program that asks the user to give it commands in the terminal. What if the user says exit? You would want an if-statement to check for something like that and then execute whatever code necessary.
Again, you do your best learning by doing. Feel free to take notes, but I strongly suggest you do all the exercises The Odin Project suggests and then some to help you grow as a developer.