the fax has greatly changed office work, especially in china. when you place a sheet of paper in a fax machine, the machine "reads" the writing on the page and changes the shapes of letters into electronic signals. it then sends these signals down an ordinary telephone line to another fax machine, which changes the signals hack into the shapes of letters.
you can imagine how usful this is, particularly in countries like china and japan, which use written characters not letters. it is also useful for sending pictures, designs, maps and so on.
sending a fax in more expensive than posting a letter, but much quicker. for example, you can send information abroad immediately, but mailing a letter might take a week or so. if you want to send a letter to an office abroad that is in a different time one, you can send a fax, and it will be received even though the office is not open.
there are two other points to consider. first, remember that a fax can be read by anyone,so be careful what you send! second, do not start faxing everything! it is much cheaper to post or email a long report than to fax it.