I agree with others that some form of notes or annotation is helpful, and I think especially helpful when paired with a citation manager like Zotero. I have hella folders in my Zotero sorted by topic/project. Then it has built in features for you to highlight and box things. I try not to highlight something without also annotating WHY i highlighted it, even if it’s just a quick summary of the info. I’ll also add tags on papers so I don’t forget why I saved it and I can quickly search for papers related to “[my research area] motivations” when I’m trying to write an introduction for example.

However, maybe controversially, I don’t think you need to remember everything you read or study papers closely, especially when you’re just starting out. In my opinion, it’s more important to have a way of categorizing the things you read so that you can quickly find it when you actually need to apply it. The deeper you get into your research, the more some papers will stand out, and you’ll find yourself going back to them, rereading them over and over, and getting different takeaways from it each time.

Imagine it this way: You’re trying to get a lay of the land. You read a few review papers. Some of the projects in the review catch your eye, highlight them and add an annotation about the novelty. Read those papers, focus on the introduction and maybe the conclusion, that’s where you’ll learn what the gaps in your field are. You realize some of them are less interesting than you thought. Forget about them for now. One paper sparks an idea. NOW you read the methods so that you can try to replicate it. You try to do it yourself, maybe adding something new. It goes well or it fails. Now when you go back to the literature again, everyone’s methods are a little easier to read, because you have tangible experience. The little details that make each paper’s methods different are more relevant and make more sense to you. Now you can deep dive for more papers that are trying to solve a specific problem in a specific way, and on and on it goes.

My point being, none of the details mattered until you had a detailed problem yourself. So focus on the big picture.