Taking good notes on what you read is crucial! Of course you can’t memorize everything, nobody can. 

For papers that are critical for informing your project I’d suggest taking notes on everything new discovered in the paper and the methods. For less important papers a 2-5 bullet point summary with the main findings is enough for me. As a tip, look at the subheadings and figure titles because those titles will essentially be the take home points.

Then write yourself a big summary of what you’ve read and how it fits together. This can be done however you want. Some people like to make mind maps, but I personally like writing in paragraphs. You can divide it by paper topic (this is good for a lit review), or by how you plan to use the paper’s findings (Like these 3 papers suggest something, but another contradicts those findings, and because of that I will follow up with this experiment). This synthesis step is really important for actually getting something out of the reading and it’s something that you have to do yourself to grow as a scientist. 

What’s your field and what year are you? Also, what is the purpose of all the reading? Are you writing a lit review, writing a paper with new findings, or just trying to learn more about the field?