Formulae usually work like this:

• There are many functions built into Excel, some of which will be covered later.  "SUM" is one of the most useful.
• In the above graphic, (B3 : E3) should be read as : "From cell B3 to Cell E3".  The colon separating the "B3" from the "E3" indicates a RANGE of cells
• NB  You do not need to type in this range.  When you«ve opened the brackets, like this...
  simply click and drag over the cells you wish to include in the calculation, and excel will insert the range for you.