Assuming you’re genuinely asking and may also be a beginner, I highly recommend reading this textbook:
http://www.boydnlo.ca/wp-content/uploads/2020/10/Optics-in-Our-Time.pdf
(Free by the way- if the link doesn’t work just search up Optics in our Time) It really helped me get through it !! (If it’s not enough, I also recommend QED by Richar...... reply
