A function takes inputs, called arguments, and creates an output. There are hundreds of functions available in Sheets.

Some functions take only one argument, or none at all.

SUM(range)values being added
AVERAGE(range)values being averaged
COUNTA(range)cells in which to count data values
ISBLANK(cell)cell that may or may not be empty

Some functions take two arguments.

FunctionFirst ArgumentSecond Argument
HYPERLINK(url, link label)web addressclickable text
CORREL(range1, range2)range of x valuesrange of y values
COUNTIF(range, criterion)range of cellsrequirement needed for a cell to be counted
RANK(value, range)value being rankedrange of values first argument is being ranked against
    ➜ Try it
  1. Type =SUM(I4:I400) in cell I3.
  2. Type =HYPERLINK("","Help") in cell I2.