how many types of cell references are available in excel

You can use three types of cell references in Excel 2010 formulas: relative, absolute, and mixed. Using the correct type of cell reference in formulas ensures that they work as expected when you copy them to another location in the worksheet. Formulas and functions are at their most useful when using references, so you need to understand them.
Excel is dynamic when it comes to cell addresses. If you have a cell with a formula that references a different cell’s address and you copy the formula from the first cell to another cell, Excel updates the cell reference inside the formula.

Excel has three addressing modes: Relative, Absolute and Mixed.
A Relative address will reference the same cell in relation to any cell where it is copied. For example cell B3 is one cell to the right of A3, so when you copy the formula =A3 from B3 to C5, it will now read =B5.

References:

http://support.jetglobal.com/hc/en-us/articles/219403207-Excel-Cell-Reference-Modes?mobile_site=true
http://library.soton.ac.uk/sash/dissertation-planner/writing-literature-review