The Dock only appears when You are in the Overview and App Grid; it doesn't appear on the normal Desktop. Push the Super Key (Windows Key) to come to this.
If You want a Dock on the Desktop You could use the Gnome Extension called Dash To Dock. You can install it from the Gnome Extensions Website or use the Extenson Manager what You can find in Gnome Software. It is a nice Program to manage and install Gnome Extensions.