I happened to reply to a certain person in PC how conversions between hexadecimal and binary number systems work, so I thought I might as well copy the information here. It's pretty simple really.

Every hexadecimal digit (0, 1, 2, ..., D, E, F) is described in binary with 4 bits.

Code:

binary = hex (dec)
---------------------
0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = A (10)
1011 = B (11)
1100 = C (12)
1101 = D (13)
1110 = E (14)
1111 = F (15)

Now if we for example wanted to describe the hexadecimal number 6B in binary, that would be:

Code:

binary = hex (dec)
---------------------
0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
*0110 = 6*
0111 = 7
1000 = 8
1001 = 9
1010 = A (10)
*1011 = B (11)*
1100 = C (12)
1101 = D (13)
1110 = E (14)
1111 = F (15)

0110 1011