They are essentially little pictures, often made with letters and words, which cryptically represent a word, phrase, or saying. Here are five of the main ways in which a rebus puzzle might encode its solution.
One of the most common devices is the positioning of the words and symbols, both relative to the rectangle containing the puzzle, and to the other words and symbols. In the example MAN is in MOON, so it is the man in the moon.
Often attention is drawn to some part of the picture, often by an arrow or underlining, indicating that this is where we should be looking for the clue. Here the arrow points to the first AID, and thus the answer is first aid.
Unusually large or small words or symbols may be used to convey concepts like big, large, small, wide, etc. For example, the rebus puzzle on the right represents big deal.
If a word or symbol is not printed in black, then you can expect the color to be a relevant in the solution. More difficult rebus puzzles may make use of somewhat more obscure colour names like scarlet or beige. In this fairly easy example CHEESE is blue; it is blue cheese.
The device of number is frequently exploited, due to the closeness in sound of 0, 1, 2, 4, 8, 10, etc. to other English words. This cryptic example shows 4 GOT 10 HEROES, and so the answer is forgotten heroes.