The encryption flow is shown in the following figure. It consists initial permutation, 16 rounds of process using round keys and final permutation.
The decryption uses the similar flow in encryption, except the round keys are in reversed order.
The function f used in encryption and decryption is depicted in the following figure.
Key schedule generates 16 round keys from original key. The process consists of an initial permuted choice and 16 rounds of left shifting and permuted choice.
The 3DES encryption flow is shown in the following figure.
The 3DES decryption flow is shown in the following figure.
