how to connect a projector

What Mac do you have?

For most, you are going to need some sort of adaptor. This could be a Mini DisplayPort to DVI or MiniDisplay Port to VGA, depending on what input the projector supports.

it is a mac book air 11inch with mavericks. I have attached the mini display port to vga adaptor and attached that to the projector

same situation mang10. And it says there is no signal... ;(