How do they work?

Hi Sevi, Welcome to the forum, Thank you for your post, in answer to your question:
I am a big fan of Pivot Tables. Unfortunately a lot of people tend to shy away from Pivot Tables, as they see them as too complex. To be honest with you, when you first use a Pivot Table the whole thing can seem a bit daunting. Don't be put off by this as persistence will almost certainly pay off.
I find the best part about Pivot Tables is their ability to be manipulated via 'Trial-and-Error' and immediately show the result. If its' not what you expect, simply use the Undo feature and/or have another go!
What you must always remember is that you are not changing the structure of your original table in anyway at all, so you can do no harm!
Why are they called Pivot Tables ? - Well, basically they allow us to pivot our data via drag-and-drop to produce meaningful information. This makes Pivot Tables interactive in that once the table is complete we can very easily see what effect moving (or pivoting) our data has on our information.
Believe me, no matter how experienced you get at Pivot Tables there will always be an element of trial-and-error involved in producing the desired results! What this means is you will find yourself pivoting your table a lot!
What would we use them for?- We would use a Pivot Table to Summarise data, or to produce meaningful information from a large table of information.
Imagine you have a table of data that contains names, addresses, ages, occupations, phone numbers, postcodes etc. With a Pivot Table you could very easily and quickly find out:
1. How many people have the same names.
2. How many postcodes are the same.
3. A count of a particular occupation.
4. See only people who match a particular occupation.
5. Find out the addresses of people that match a postcode
In fact the list can go on and on!
The most important factors when considering using a Pivot Table is to have your data set up in what is called a table and/or list. As your Pivot Table will be basing all its data on this list or table it is vital that you set your tables and lists up in a uniform way.
In the context we are discussing here, a Table is no more than a List, with more than one Column of data and a different heading for each column. The 'good practice' that applies to setting up a List will aid you greatly when you need to apply a Pivot Table to your Data.
When we use Excels built-in features they will and do assume a lot about the layout and setting up of our data. They do have a degree of flexibility but more often than not you will find it easier to follow the guidelines for setting up your Table or List.
Let's look at what I believe to be the most important aspects of setting up a Table or List.
Headings. This is a must! They should always be in the row directly above your data. Never have a blank row between your data and the headings. Make them distinct in some way eg; Bold them.
Leave at least three blank rows above your headings. These can be used for formulas, critical data etc. You can hide the Rows if you wish.
If you do have more than one List or Table on the same Worksheet leave at least one blank column between your List and Tables. This will aid Excel in recognising them as separate. However, if the lists and tables are related to each other why not make them into one large table.
Avoid blank cells within your data. Rather than leaving blanks for the same data in a column repeat the data as many times as needed.
Sort your List or Data, preferably by the left most column. This is not so much for the Pivot Table's benefit, but for the person reading the data.
If you follow these guidelines as close as possible, using Pivot Tables will be a relatively easy task.
I hope that has helped, if so please click the Resolved link, best regards Pete