The SUMIFS function allows users to sum a range of cells based on multiple criteria. It can check multiple criteria ranges, unlike the SUMIF function which only checks one criteria. Operators like >, <, = can be used in criteria. The syntax includes specifying the sum range, criteria ranges, and criteria. Examples demonstrate summing values where corresponding cells meet criteria like being greater than 1000 and equal to "East". Cell references can also be used for dynamic criteria evaluation.