First remember that a lot of people who seem to pick things up quickly also forget things just as quickly. Understanding is not just knowing a bunch of facts but how they relate to one anouther. It has been my obesrvation that the slow learner is the one who is smarter in 20 or 30 years. One sugestion is to review every day. Go over your notes, do the extra resurch. I still do that I am always looking things up and I listen to others who think they are so smart and I wounder if they realy live on the smae planet.
Figure out how you learn best. some people have to do, others have to be showen, some people understand best from reading or from an explanation. The more ways you approch things the better. I would take notes in class but could never look at them again, just taking them was enough.
3000 years ago some one put it this way, "Line upon line, precept upon precept, hare a little there a little" There is a movie called "born yesterday" get it, watch it. It is about a woman who was a slow learner who out smarted every one.
Everyone takes their time, its not something wrong.
Best thing to do is to read things over till you understand it, and when you dont get something make sure you get individual help, if it's in school you can try asking for help after school, or meaby go online and search stuff over and with more explanation.
Make a daily routine of positive auto-suggestion,effort to be quick learner and believe in self that makes you better.
listen to the words carefully.