We start from number one always multiplying it by two. We get numbers 1,2,4,8,16,32,64,128. Eight numbers. Then we make a table:
Remember, 0 is OFF. 1 is ON. Now the binary is 0 because every number is turned off. Lets turn something on.
Now two values are turned on, and guess what; just simply calculate the numbers together. Number two is ON so we have 2 and the number 8 is turned ON so we have numbers 2 and 8. 2 + 8 = 10. The binary value is ten. Simple as that.