Lighting, Light Fixtures, Ceiling and Exhaust Fans - Help with outdoor light

I am replacing an older outdoor light fixture. I just took off the hardware and it has a yellow wire and a black wire. The new light I am replacing it with has a white, black and copper. Instructions state black to black, white to white and ground wire house ground wire to the mounting strap witha green ground screw.

So do I attach the yellow to the white, black to black and copper to the mounting strap? And, what is the mounting stap, just the casing? And, do I just go to a hardware store and buy a green screw?

Never done any electrical other then changing a light bulb so had to ask.

Look more closely at the "yellow" wire. Is it really yellow, or was it perhaps originally white and it yellowed with time (and, unfortunately, overheating)?

You are right, the wire is yellowish, but it is white. But what about the green ground screw?

Okay, so it's black to black and white to white. The grounding wire from the fixture can be connected to some metallic part of the mount. It might not go any good, but it won't hurt. Normally, the mounting strap is a flat piece of metal that comes in the package with the fixture. This piece of metal often has a green screw on it. If so, you can connect your grounding wire there.