Warm Colors are the ones that remind you of heat and warmth, like reds, yellows, oranges, etc. These colors tend to feel cozier, friendlier, and more cheerful. You can introduce more warm tones to a picture by increasing the yellow / orange tones in your photograph.
Cool Colors are the ones that remind you of colder temperatures. These generally tend to create a calm and serene atmosphere. You can inculcate cooler tones to a picture by increasing the blue tones in your photograph