In terms of features, NeoOffice (donations accepted) is huge, truly a viable alternative to Microsoft office. It includes all the basic components: Writer, the Word processing component; Calc, for spreadsheets; Impress, the presentation module; draw, for the creation of graphics and diagrams; and Base, the database component. The spreadsheet component has some sophisticated features like Advanced DataPilot technology, Natural language formulas, an Intelligent Sum Button and a comprehensive range of advanced spreadsheet functions.
You will find that there are dozens of different tutorials available online, ranging from books and courses that you can pay for to tutorials and video lessons that can be downloaded for free. Each of these courses is broken down into sections that will address each of the different sections of formula so that you can learn them in groups. This tends to make it much easier to fully grasp the necessary formula for each section before moving on to the next segment.