I want to ask questions about the effect of anxiety and stress on memory and learning. can feeling anxious while studying make it difficult to understand and remember things? thank you?

That is all part of anxiety and stress. If this is a one-time event, try to take some time out to relax - go for a walk (or run), try to sit quietly for 30 min and let your thoughts drift, talk with a friend (about a TV series, a new restaurant, etc - NOT about your studies). Only if this is happening over and over should you seek professional help

Yes, anxiety and stress can have a negative effect on memory and learning. Please see a Clinical Psychologist with expertise in multiple types of psychotherapy to help you cope and a Psychiatrist can help with medication. Also have a physical exam to rule out illness.