I need help on the below Triple DES figure please. I'm stuck.

Question: From the figure below, please explain what it represents in sufficient detail. Explain it as if you are explaining to someone who does not understand network security. Thank you

This is what I know about the figure

C stand for = ciphertext

P stand for = plaintext

E[k, X] stand for = encryption of X using key K

D[ K, Y] stand for decryption of Y using key K

K1 E K3 D A B K (a) Encryption K E (b) Decryption B A K3 E K D Figure 2.3 Triple DES C P