Hi !
We use hexadecimal format because it is simple and fast to convert and represent bits sequences (binary numbers) into hexadecimal numbers. Just separate the binary digits in groups of 4 (nibbles) and each nibble will be represented by a hexadecimal digit (from 0 to F).
0000 binary = 0 hexa
0001 binary = 1 hexa
0010 binary = 2 hexa
0011 binary = 3 hexa
0100 binary = 4 hexa
0101 binary = 5 hexa
0110 binary = 6 hexa
0111 binary = 7 hexa
1000 binary = 8 hexa
1001 binary = 9 Hexa
1010 binary = A hexa
1011 binary = B Hexa
1100 binary = C hexa
1101 binary = D hexa
1110 binary = E hexa
1111 binary = F hexa
Then to represent the byte 10010011 you just separate 1001 and 0011 and convert into two digit hexadecimal format: 93h , you notice that a byte can be represented by two hexadecimal digits.
As for computers, the binary format is better and decimal is better for humans, the hexadecimal is a mid term and can save digits when reprsenting large numbers, for example: 65535 decimal may be represented by FFFF hexa, saving one digit compared to decimal base.