Tableau holds a set of ready-made analytical tools that can be simply dragged and dropped onto a view. Those functions can be found in the Analytics pane, usually by clicking on the tab next to Data:

If you can't see this on the left-hand side of your screen, you can go to Window > Show Side Bar in the menu bar to display it. The pane holds tools that have been separated into three sections: Summarize, Model, and Custom.