Hi
In Calc you can find a Σ sign below the menus, just beside the long white field where the formula is shown, immediately above the cells of the spreadsheet. Sometimes the area it selects by default is not quite perfect so you can just drag-select the area you prefer.
You might find this guide helpful
https://wiki.documentfoundation.org/Documentation/Publications#LibreOffice_Calc_Guide
The 4.0 branch is only half complete but the guide for the 3.4 branch is plenty good enough. At this level you probably wont notice many changes anyway. The changes in Calc tend to be quite advanced stuff, even such as smoothing of types of curves in charts.
Errr, you had written to the wrong list. The documentation team 'just' focus on writing the guides. It's a small team with a ton of work that they get through amazingly fast. It's the Users List that answers people's questions. So, i have forwarded your question there and let the Docs Team know they don't have to worry about spending time on this.
On the other hand if you could help proof-read some of the newer versions of the chapters, as they come out, that would be enormously helpful. One of the criticisms of Guides and Manuals generally is that they are written by people that are NOT new and so a lot of technical words or strange phrases creep in. Unfortunately, everyone who does join in with the work in the Docs Team quickly becomes fairly expert so we constantly need new people to join in.
Regards from
Tom