The Microsoft Office Suite is the most popular office suite for the PC. The most popular features are Word and Excel. You also get an email reader and, depending on the version you purchase, data base management, presentations, project management, and other things.
The suite is powerful and the cost is high. There are, however, free alternatives. Wikipedia has a good comparison chart of alternatives, some free, some at a nominal cost, and others at a ridiculously high price. Here's some of the free ones. These all contain at least a word processor, a spreadsheet program, and a presentation program. Clicking on the program name will bring up the Wikipedia article on it. A link is also provided for each program's home page.
IBM Lotus Symphony website
GNOME Office website (Note: Gnome's integration among the word processor, spreadsheet program, and presentation program isn't as tight as what you would expect from an office suite.)