Unknown representation of number as bits
They've split an 8-bit byte into two four-bit nibbles (sometimes spelled "nybble").  The brackets denote multiplication; it's just saying that
$$10110010 = 10000\times 1011 + 0010\,,$$
(written all in binary to avoid having two different bases in the same expression).  This is just like saying, in decimal, that
$$837\,487 = 1000\times837+487\,.$$
There isn't really anything to find out.