Although the Raspberry Pi can be connected to a TV or monitor via HDMI or DVI, there are times when running a Raspberry Pi “headless” (without a monitor) is desirable. In a headless setup, you could connect to your Raspberry via SSH but if you want the full desktop then you will need to connect using a remote desktop protocol. The easiest is to setup VNC on Raspberry Pi. Virtual Network Computing (VNC) is a graphical desktop protocol that allows you to access the full Raspberry Pi desktop from another machine. Typically you would run the VNC client on a PC running Windows, OS X or Linux and access the Pi’s desktop over the network.

Full article here:
Setting up VNC on Raspberry Pi (Make Tech Easier)

Related link:
VNC Starting Automatically on Raspberry Pi (School Pi Club)