It's not something you try to recite. You just do it so many times you became too good at it to look at the table.

Four bits can represent up to 15, from 0000 to 1111. Correspondingly, 0 to F in hex.

Binary from right to left is 1, 2, 4, 8.

One byte is eight bits. It takes eight digit places.
XXXX XXXX

0000 0000 to 1111 1111
00 to FF
0 to 255