The dock doesn't quite work that way, as you may have many other choices (depending on the particular app.)
Certainly you can just click on the icon to launch the app.
The key is the right-click. You also get the menu if you just click and hold the icon in the dock - no right-click is usually needed - and choose what you need from the menu.
That menu gives you all the choices. You can also use the keyboard shortcut Command-H to hide the app in front, etc.
There could be a third-party utility that allows you to re-direct the default action when clicking on the Dock icons, but I haven't heard of that as a feature.