I would say don't worry about it if you can't remember how to do things on your own. As long as you are able to read the code, and make sense of it, you are on the right track. After you need to use something 5-10 times, and you have to keep going back to look at how to do it every time, it will solidify it in your brain more, and eventually, you will remember how to do it without even looking.
I remember the first time I worked on a project where we had to set up encoding and decoding data, and I thought there was no way I would ever remember how to set all that up on my own. Now I have done it so many times, I can write a struct that conforms to Codable without even having to look at examples. (Although, the autocomplete suggestions in XCode definitely still help) Remembering on your own will come with time and practice.
Learning to read Apple's documentation is something else that will come with time. Even if you feel like it is usually too hard to read and you don't usually gain anything from it, keep trying to take a look at their pages when you run into problems with certain things. At first it is confusing to look at. But, as you progress in your learning and learn more coding lingo, you will start to see patterns in how it is organized, and know the names for things that make it more understandable. Soon enough, you'll be able to read the pages with a near complete understanding. Well... maybe not soon... but some day!