Firstly we make pairing of 4 binary numbers from right side of the binary expression, assign 0 to the leftiest pair if it turns out to be less than 4 digits, then assign respective numbers/alphabet from the chart below for each pairing. Then enclose the result withing a bracket with base 16.

For example we want to change the decimal expression (1011011011011110000)2  into hexadecimal, (which is itself the binary expression of decimal number 374512).

Making this binary expression into pairing of 4 we get:
101    1011    0110    1111    0000

The leftiest pair doesn't have 4 digits, so we add 0 to the left of it.
0101    1011    0110    1111    0000

Now use the following table to assign respective numbers/alphabet to each pair:

Changing 0101    1011    0110    1111    0000  into hexadeciaml we get

5 B 6 F 0
Enclose this within a bracket with base 16.
(5B6F0)16  is the final result.