Binary addition of bits is easy:

 0 + 0 = 0
 0 + 1 = 1
 1 + 0 = 1
 1 + 1 = 10  (10 in binary is 2 in decimal)

Binary addition of unsigned integers:

E.g. unsigned byte integers
     x = 0x07
     y = 0x03

The sum is of course 10 or 0x0A in hex. 

In binary:

carry bits:      111   
         x: 0000 0111
         y: 0000 0011
            ---------
       x+y: 0000 1010

or in hex x + y is 0x0A