These are some of the most fundamental and useful functions in Excel! Here's a quick breakdown of how to use SUM, AVERAGE, and COUNTIF:

SUM Function:

* Purpose: Calculates the sum of values within a range of cells.
* Syntax: `=SUM(range)`
* Example: Let's say you have sales data in cells B2:B10. To find the total sales, enter `=SUM(B2:B10)` in an empty cell. Excel will add the values in B2 through B10 and display the sum.

AVERAGE Function:

* Purpose: Calculates the average of values within a range of cells.
* Syntax: `=AVERAGE(range)`
* Example: You have exam scores in cells C3:C8. To find the average score, enter `=AVERAGE(C3:C8)` in another cell. Excel will calculate the average of the scores in that range.

COUNTIF Function:

* Purpose: Counts the number of cells within a range that meet a specific criteria.
* Syntax: `=COUNTIF(range, criteria)`
* Example: You have a list of fruits in cells A1:A15. If you want to count the number of times "Apple" appears, enter `=COUNTIF(A1:A15, "Apple")`. The quotes are important to specify the exact text you want to count.

Additional Tips:

* You can use cell references instead of ranges by directly entering the addresses of the cells you want to include in the calculation.
* Excel allows for nesting functions within formulas. For example, you could calculate the average of the sum of two ranges using `=AVERAGE(SUM(A1:A5),SUM(B1:B5))`.
* Explore other basic functions like COUNTBLANK (counts empty cells) and COUNTIFS (counts cells meeting multiple criteria).

Remember, these are just a few of the many powerful functions available in Excel. Experimenting and exploring will help you unlock the full potential of this versatile tool.