An input text form field is presented with a accompanying label describing what input is expected in the field. The label describes a specific structure the user must follow to input a valid value.
It is often seen that the user is also presented with the possibility to use helping mechanisms such as a date selection calendar to fill out the input box in the correct way. When the user has done this multiple times, he or she slowly learns how the input is formatted correctly by the helping mechanism, so that they can copy the same format on their own.
Using a structured format in an input field saves time for the user, who fills out the same input field repeatedly as a part of a frequent task. Instead of having to go through half a dozen of select and checkboxes, the same input can be typed much faster if a specific input text structure is followed.