In Europe, the port-side buoys have a cylindrical shape and are red. Coming back from the sea, they have to be kept on the port-side (left), i.e. you should pass to the starboard-side (right) of the marker. The starboard-side buoys have a cone shape and are green. Coming back from the sea, they have to be kept on the starboard-side (right), i.e. you should pass to the port-side (left) of the marker.
These sailing terms date back to the 15th century and originate from the Netherlands. In those days, sailors steered their boats with the help of a rudder, fixed on the right of the vessel when looking towards the bow of the boat. The rudder's side was called stierboord ("stier": rudder, "boord": side). When navigating like this, sailors had their backs to the left side, hence bakboord ("bak": back, "boord": side).