Long-tapping on the home screen is how widgets used to be added in earlier Android versions, up to about 2.1. Some devices (such as Samsung ones) still offer the old way on the manufacturer's stock home screen: adding widgets is a feature offered by the launcher, so some third-party launchers may have yet different ways.
On the stock Android launcher, go to the app drawer (the list of all apps), and click Widgets at the top. Find the one you want (there are several pages), and long-tap it to pick it up, then drag and drop to the space you want on the home screen. You can drag to the left or right edge to change home screens. Once you've dropped it, you can drag the blue highlight to resize the widget (if it's resizable).