54 is a number represented in decimal (base 10). Binary (base 2) numbering is a simple system where the only two valid digits are 0 or 1. Whereas, in base 10, the numbering columns are ones (far right), tens, hundreds, thousands (working from right to left), in base 2, the numbering columns are one, two,four,eight,sixteen,thirty-two,sixty-four, etc. Some more concrete examples follow:
in base10 the number 54 in decimal is 5x10+4x1
Binary is base2 math, so the numbering columns are ones(2^0), twos (2^1), fours (2^2), eights (2^3), sixteens (2^4), and so on. The only two valid digits in base2 are 0 and 1, so the number 54 doesn't exist because you can't have a digit higher than 1... but the decimal value 54 would be expressed as follows:
110110 -- that is 1x(2^5)+1x(2^4)+0x(2^3)+1x(2^2)+1x(2^1)+0x(2^0)
Octal is base 8, so the numbering columns is
ones (8^0), eights(8^1),sixty-fours(8^2), five hundred twelves (8^3) [again, from right to left]. The only vaid digits in base 8 are 0 - 7
So, to express 54 as octal, is 66 -- that is 6x(8^1)+6x(8^0) or 48+6
Hexadecimal is base 16 so the numbering is 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
and the numbering columns is ones (16^0), sixteens (16^1),
two hundred fifty-sixes(16^2), four thousand ninety-sixes (16^3) and 54 in hexadecimal is expressed as 36 -- that is 3x(16^1)+6x(16^0) = 48+6 = 54.
I hope this helps explain the numbering systems with some concrete examples.