A 4-Square looks like this:
4-Squares are used by dealers because they make consumers feel obligated to purchase a vehicle at the agreed-upon terms, even if the details of the deal are not explained when they signed the 4-Square. Dealers also use 4-Squares to trick consumers into focusing on the down payment and monthly payments rather than the price of the vehicle. If you signed a 4-Square containing the price of a vehicle, payments, or other terms, the dealer may have broken the law.
You can protect yourself by keeping a copy of all paperwork that you signed. Or, take a picture of it with your phone.