Guess focusing was the most common way of focusing during many years. You had to estimate the distance to the subject yourself, and set the focusing ring or focusing lever accordingly. You were somewhat assisted by the depth of field scale. Usually the lens was fixed and its aperture was not too big, typically f/2.8 as a maximum. It is not possible to guess the distance with enough precision for a larger aperture.
These cameras were usually more expensive than the fixed focusing ones, but cheaper than the rangefinder or reflex type.
A variant was scale focusing, used on cheaper cameras, targeted to people who would not take the trouble to guess a distance in meters or feet. Symbols on the focusing ring, (usually "one person", "a group of people" and "a mountain") indicated the most probable setting for your picture depending on the subject.
This range of camera has evolved to become the point and shoot cameras, equipped with an autofocus device, consisting of an infrared light emitted by the camera and reflected by the subject (note it might differ on the digital ones?). You do not have to guess the distance yourself, and of course the operation is faster.