Let's first take a look at decimal addition.

As an example we have 26 plus 36,

26
+36

To add these two numbers, we first consider the "ones" column and calculate 6 plus 6, which results in 12. Since 12 is greater than 9 (remembering that base 10 operates with digits 0-9), we "carry" the 1 from the "ones" column to the "tens column" and leave the 2 in the "ones" column.

Considering the "tens" column, we calculate 1 + (2 + 3), which results in 6. Since 6 is less than 9, there is nothing to "carry" and we leave 6 in the "tens" column.

26
+36
62

Binary addition calculations work in the same way, except that only 0's and 1's can be used, instead of the whole spectrum of 0-9. This actually makes binary addition much simpler than decimal addition, as we only need to remember the following:

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 10

As an example of binary addition we have,

101
+101

a) To add these two numbers, we first consider the "ones" column and calculate 1 + 1, which (in binary) results in 10. We "carry" the 1 to the "tens" column, and the leave the 0 in the "ones" column.

b) Moving on to the "tens" column, we calculate 1 + (0 + 0), which gives 1. Nothing "carries" to the "hundreds" column, and we leave the 1 in the "tens" column.

c) Moving on to the "hundreds" column, we calculate 1 + 1, which gives 10. We "carry" the 1 to the "thousands" column, leaving the 0 in the "hundreds" column.

101
+101
1010