Most docking stations that are not dedicated to a model connect to a USB port (3.0 is better) and provide up to six USB ports, two different display ports (usu. HDMI and DVI), mike and speaker ports, and a RJ-45 port for gigabit ethernet.
Better ones support two different displays (at least 1920x1080) but less expensive ones just provide two outputs that are the same. I also look for at least a 4A power supply (6A is better).