Do I need to use any wood protector for my deck?
Some wood species hold up well outdoors even without a surface treatment (like cedar and redwood). I can't tell by the photos what type of wood your deck is made of. That being said, it certainly would not hurt to treat it. It would help stabilise the the color and protect the wood.

The type of coating is up to you, but my preference wood be a high quality semi-transparent stain. The amount you need depends on size and various other factors, follow the directions on the can.