how can i stream video and audio from macbook air to my tv?

Wirelessly: you need an AirPlay - enabled device such as an AppleTV.

Wired: if your TV has an HDMI port, you need a Thunderbolt to HDMI adapter such as this one:

Mini DisplayPort to HDMI® Adapter w/ Audio Support

If your TV does not have an HDMI port you will need a converter that will convert HDMI input to whatever input your TV requires.