Often, we will use formulas to generate a table of values, as for a function. We use filling down to keep from having to enter the formula in each cell individually. It's very similar to the the Fill Series technique used to fill in a sequence of numbers in a column.
Let's create a table of values for the function f(x) = x^{2}  2 x + 1. First, we fill in the x values in a table using the Fill Series technique:
A 
B 

1 
x 
y 
2 
0 

3 
0.5 

4 
1 

5 
1.5 

6 
2 
In this case, we choose to use x values from 0 to 2 with a step value of 0.5.
Next, we enter the formula for y in the first cell in the y column, which is cell B2. Since the x value is right next to us in cell A2, we use the formula =A2^22*A2+1, using A2 for x.
Now we copy down in one of two ways:
Edit> Fill > Down 

Dragging down 

In both cases, if you go back and inspect the formulas in column B, you will find that the formula has changed as it was copied down. Cell B3 for example, has the formula =A2^22*A2+1. This is because we have used a relative reference. Relative references tell Excel what the address of a cell is relative to the current cell, so that you can copy a formula to another cell and have it behave in the same way. See Relative and Absolute References for more information on this.