1. Excel Functions

2. WHAT IS AFUNCTION
A function in excel is a preset formula that performs calculations automatically
The general syntax of function is as follows:
=function name(argument list)

3. To use a function follow the Steps below
Select the cell to display the result
Insert the function from formulas tab
Function argument dialog box appears
Select the cell range from the worksheet
These steps work for most functions

4. The SUM function, one of the math and trig functions, adds values
The SUM function, one of the math and trig functions, adds values. You can add individual values, cell references or ranges or a mix of all three.
For example:
=SUM(A2:A10)
=SUM(A2:A10, C2:C10)

5. Returns the average (arithmetic mean) of the arguments
Returns the average (arithmetic mean) of the arguments. For example, if the range A1:A20 contains numbers, the formula =AVERAGE(A1:A20) returns the average of those numbers.
Syntax
AVERAGE(number1, [number2], ...)
The AVERAGE function syntax has the following arguments:

6. Returns the largest value in a set of values.
Syntax
MAX(number1, [number2], ...)

7. Returns the smallest number in a set of values.
Syntax
MIN(number1, [number2], ...)

8. The COUNT function counts the number of cells that contain numbers, and counts numbers within the list of arguments.
syntax
COUNT(value1, [value2], ...)

9. The COUNTA function counts the number of cells that are not empty in a range.
Syntax
COUNTA(value1, [value2], ...)

10. The COUNT function counts the number of cells that contain numbers, and counts numbers within the list of arguments. 

11. Use COUNTIF, one of the statistical functions, to count the number of cells that meet a criterion; for example, to count the number of times a particular city appears in a customer list.
In its simplest form, COUNTIF says:
=COUNTIF(Where do you want to look?, What do you want to look for?)
For example:
=COUNTIF(A2:A5,"London")
=COUNTIF(A2:A5,A4)

12. You use the SUMIF function to sum the values in a range that meet criteria that you specify
Syntax
SUMIF(range, criteria, [sum_range])
The SUMIF function syntax has the following arguments:
range   Required. The range of cells that you want evaluated by criteria. Cells in each range must be numbers or names, arrays, or references that contain numbers. Blank and text values are ignored. The selected range may contain dates in standard Excel format.
criteria   Required. The criteria in the form of a number, expression, a cell reference, text, or a function that defines which cells will be added. For example, criteria can be expressed as 32, ">32", B5, "32", "apples", or TODAY().
Important: Any text criteria or any criteria that includes logical or mathematical symbols must be enclosed in double quotation marks ("). If the criteria is numeric, double quotation marks are not required.
sum_range   Optional. The actual cells to add, if you want to add cells other than those specified in the range argument. If the sum_range argument is omitted, Excel adds the cells that are specified in the range argument (the same cells to which the criteria is applied).