To make a long addition by hand is the simplest of the four arithmetical operations.
See how the long division is carried out in the following example.

The addition problem is set up with the one number above the other. 

We add 3 and 8 together, the result of which is 11. We write 1 in the result and carry 1 over to the next column. 

We add 1, 8 and 4 together, the result of which is 13. We write 3 in the result and carry 1 over to the next column. 

We add 1, 0 and 3 together, the result of which is 4. We write 4 in the result. 
The result is 431.
Long addition
Please enter the two numbers you want to add.
Decimal number
The same method is used, if you are adding decimal numbers.
It’s important, though, that the addition problem is set up, so that the digits of the same decimal place are right above each other. The best way to achieve that is to make sure that the decimal points of the two numbers are right above each other.
How the addition problem 3.14 + 41.3 is set up