The red one is a cover for a screw-hole, into which a tow fitting can be attached. A tow fitting is a small ring, welded to a bolt. You screw it into that place in the bumper, allowing a tow truck to attach to the car without having to climb underneath, potentially hooking to a part of the car that can be damaged.
The yellow ones are covers for the headlight washer nozzles. This is usually optional for higher-end cars. If equipped, when the windshield washer nozzles are activated to squirt washer fluid at the windshield, these nozzles also squirt washer fluid at the headlights. In some cars, they are hidden in the bumper when not actually squirting washer fluid.