copy (replicate) cells using both absolute and relative referencing

Relative Cell References

This is the most widely used type of cell reference in formulas. Relative cell references are basic cell references that adjust and change when copied or when using AutoFill. In more simple terms, the cells are adjusted using the same formula from the previous cell references to the other cells intended to be adjusted and changed according with the formula.

Example:
=SUM(B5:B8), as shown below, changes to =SUM(C5:C8) when copied across to the next cell.

Absolute Cell References
Situations arise in which the cell reference must remain the same when copied or when using AutoFill. Dollar signs are used to hold a column and/or row reference constant.

Example:
In the example below, when calculating commissions for sales staff, you would not want cell B10 to change when copying the formula down. You want both the column and the row to remain the same to refer to that exact cell. By using $B$10 in the formula, neither changes when copied.

http://web.pdx.edu/~stipakb/CellRefs.htm