http://www.contextures.com/xlFunctions01.html Visit this page to download the sample file for this video.

You can Sum numbers with a single click, to create grand totals. Use the SUM function to avoid errors if some cells contain text.
Use the SUMIF or SUMIFS functions to sum cells based on single or multiple criteria. Combine the criteria with wildcard characthers or operators, for more flexibility.
You can even Sum just the numbers that are visible in a filtered list.

00:00 Introduction
00:09 1. Quick Grand Totals
00:45 2. Sum Specific Cells
01:56 3. Running Total
03:28 4. Sum Specific Items
04:41 5. Sum Partial Match
06:21 6. Sum With Multiple Criteria
07:46 7. Sum in Filtered List
09:27 Get the Sample File

Watch this video to see 7 different ways that you can use functions to Sum in Excel. Included are simple examples of the SUM, SUMIF, SUMIFS and SUBTOTAL functions.