Can someone please explain the difference between the two?
AP Computer Science A is straight up programming and focuses on technical knowledge. The test is based on your ability to write in and understand Java as well as some of the underlying programming concepts.
AP Computer Science Principles is much broader and much more superficial. It shows you different applications of CS and how it intersects with business, the entertainment field, cybersecurity, etc.
AP CS Principles is an introduction to all the fields that relate to CS.
AP CS A is more specialized. It’s straight programming. If you’re really into programming it can be an easy course but you don’t like it, it won’t make you like it 
It’s good to have if you’ve got zero programming experience and you want to major in CS/Engineering in college.
CSP covers concepts such as abstraction, algorithms, security, networking, data, etc. Specifics like DNS, IP addressing, RGB coding, data structures, etc. are covered. Programming is typically lightweight JavaScript.
I wouldn’t call it more superficial as it’s completely different. CSA is a Java programing class.
They are two completely different classes. CSA tests programming concepts and your algorithmic thinking. CSP is much more broad with concepts covering many different aspects. You can read about all aspects here: https://apcentral.collegeboard.org/pdf/ap-computer-science-principles-course-and-exam-description-0.pdf?course=ap-computer-science-principles