Sheets are like pages in a book. The book is the file, and each file contains sheets (pages). Each sheet can hold your data.
If you look at the bottom of the sheet you can see a tab.

You can see that each tab holds the name of the sheet. The first sheet by default is called Sheet 1.
A sheet can be named to allow for ease of reference. To name a sheet simply double click on the tab where the name is.

Another sheet can be added or deleted. The new sheet can be renamed


Hold the control key whilst pressing on the left mouse key and drag to the position of where you want the copied sheet to be placed.
The position of the sheet can also be moved. By holding down on the left mouse and dragging the sheet to the position you want.
Grouping Sheets allows you to enter data one sheet, and have it replicated in exactly the same cell references (eg A1 to A10 for all sheets highlighted).
To do this click on the sheets that you would like to edit at the same time, whilst holding down the control key.

You will then see the sheets that you have selected highlighted on the tabs of each sheet.
You can now proceed to enter data for example in cell A1 and it will be repeated in all the sheets selected. You therefore don’t need to go to each sheet individually to enter the same data.