Thank is what you do to others. Appreciate is how you yourself feel. "Thank you for your correction, I really appreciate your help." Thank YOU I appreciate

Difference is slight. Thanking a person is in words expressed form of showing appreciation to that person: Friend helps you at work. You tell them: "Thank you for helping me." Appreciation is more than just expressing thanking. It is when you feel respect to person due his actions that effect you directly or indirectly: Friend helps you at work. You appreciate it. Friend helps you at work. You show appreciation with gift. Friend works with you. She has a lot of work. You ask her to help you. She accepts. You tell her: "I really appreciate that". After work is done you may tell her: "Thank you for your help" I hope that explains.

"Thank you" is customary after someone has helped you with something. "I appreciate what you've done for me" is a formal thank you.