An Excel file is called a workbook and will hold as many worksheets as available memory will allow (new file default is 1 worksheet). Worksheets can be independent of each other, in that the data in each worksheet is separate from the other worksheets, or they can be linked, which means that the data in one worksheet is used in some way in the other worksheets.
Having multiple worksheets within a workbook allows you to store different data sets together. For example, you might store each year's budget in one workbook with a worksheet for each year (these would be independent). You'll have all the data in one file if you want to review changes over the years.
Or you may be interested in analyzing information from different data sets. For example say you are interested in how unemployment rates affect wages, you may have worksheets set up like this, where analysis allows you to combine the relevant parts of each data set for analysis (these could be linked worksheets):
Or you may be collecting data from individuals and each worksheet could represent a participant in the study (each identified by a subject ID number):
You might also use one worksheet for data and another worksheet for graphs, especially if you will be using statistical software such as SPSS or STATA to analyze the data. Having graphs in the worksheet with the data can affect the importability of the data into statistical software programs, but you can eliminate those problems by importing the data worksheet and creating graphs in a seperate worksheet:
There is more than one way to save a workbook.
1. Click the save icon on the quick access toolbar.
2. Press 'Command+S' on the keyboard.
3. Go to the File tab and click on Save.