Google Sheets is a powerful spreadsheet program that allows you to perform complex computations on the data you enter into each cell. The application uses formulas and functions to do these tasks so you don't have to. A formula is an expression that you input to tell Google Sheets how to calculate the value of a cell, and a function is a predefined formula that Google Sheets has created for you.
The instructions in this article refer to Google Sheets.
Why Use a Function?
You may be wondering why you would use a function when a formula would accomplish your task just as well. Yes, a formula you create may be just as effective, but you would have to take the time to build it, while Google Sheets functions are already created, so you will save time and effort, and likely be more accurate (the more complex your formula is, the greater the chance that you'll make an error in creating it).
For example, say you want to add a row of numbers. You could enter the following formula into a cell in Google Sheets and the numbers would be added together and the result shown in that cell:
=A1+B1+C1+D1+E1+F1
A function is quicker:
=SUM(A1:F1)
Using a function becomes even more efficient if you have a large number of items you want to add together, or if your computation is more complex.
Google Sheets Function Syntax
Each function has a syntax, which is the specific order in which you must enter the elements for the function to perform the desired calculation.
Every function begins with the function name, followed by the arguments, which are separated by commas or a colon and enclosed in parentheses. The basic construction of a function and an example of one are as follows:
Function_Name(argument1,argument2)
SUM(A1,B1)
How to Use Google Sheets Functions
The fastest and easiest way to use a function is via the Functions menu.

Select the cell where you want to display the result of the calculation.

On the toolbar, select Functions, and choose one of the functions listed. There are five basic functions you can pick here, plus submenus that contain every possible function. The five basic functions are as follows:
 SUM adds the values in a range of cells
 AVERAGE calculates the average of the values in a range of cells
 COUNT provides the number of values in a range of cells
 MAX provides the highest value in a range of cells
 MIN provides the lowest value in a range of cells

Choose the cells you want to be included in your range.
To choose individual cells, rather than a consecutive line of them, hold down the Ctrl key on your keyboard and make your selections. To choose a large range of cells, hold down the Shift key on your keyboard and select the first and last cells in the range.

On your keyboard, press Enter.

The result will appear in the cell you selected in step #1.
Using Complex Functions in Google Sheets
What if you want to do something other than adding a selection of numbers? Google Sheets includes dozens of functions that perform a wide variety of tasks. For example, you can calculate the number of days or the number of working days (Monday through Friday) between two dates.
To find the right function, reference the complete list of Google Sheets functions. To narrow down the options, type a search term into the Filter field and press Enter to see your choices. For example, to find the function for calculating the number of days, use the word "days" as your search term. Two possible results are the DAYS and NETWORKDAYS functions.
Alternatively, within Google Sheets, on the toolbar select Functions and choose one of the submenus at the bottom of the list.
Some functions require you to input data in a particular way. Here's how to do it, using the NETWORKDAYS function as an example:

Select the cell where you want to show the number of working days between two dates.

Type =NETWORKDAYS.
To use this function, you don't have to have any other data in your spreadsheet.

You'll be given two options: NETWORKDAYS and NETWORKDAYS.INTL. Select NETWORKDAYS.

Now you'll see a window that shows you the correct format for entering your information. Review it, then, in the upperright corner of the window, select X to exit.

Type in the start and end dates of your date range using the same format as the formula, paying close attention to punctuation placement.

On your keyboard, press Enter.

The number of workdays will appear in the cell you selected in step #1.
Using Functions with Text in Google Sheets
Google Sheets functions can be helpful with text as well.
For example, you can use the GOOGLETRANSLATE function to translate selected text from a source language to another specified language. Here's how to do it, using the Spanish word hola as an example:

Select the cell where you want the translated text to appear.

Type =GOOGLETRANSLATE("HOLA")

On your keyboard, press Enter.

You'll see the translation in the cell you selected in step #1.