There are a few ways to get the smooth action we all want in our footage and they all have their pros and cons, Chrystopher Rhodes from YCImaging does a fantastic job at explaining three of the main ones and when to use them.
Sliders - Precise smooth motion, but limited to your track length. Great for subtle movements.
Shoulder Rigs - Gives the 'real' handheld feel without that unwatchable handheld shake. Easy to set up.
Gimbals - Not as precise as a slider, but gives you the freedom to walk (even run) with the camera much further. Trickier to set up and operate.