Small telescopes can show you something of Mars, but to see details you will need at least a 5 inch (125 mm) refractor or an 8 inch (200 mm) reflector, and long focal ratios (f/8 to f/10 or more) are preferable. Good seeing is also essential.
With Mars, unlike most planets, colored filters will really help your observations. High-quality glass filters that screw into your eyepiece are available from telescope-accessory dealers. Many observers, however, prefer to start out with less-expensive gelatin filters, such as Kodak's Wratten filters, which can be bought from camera stores.
A useful set would include a blue (Wratten 44a) or blue-violet (W47); a green (W58) or a yellow (W12 or 15); an orange (W21 or 23a); and a red (W25). To use these filters, simply hold them up to the eyepiece and look for features that appear enhanced.