Residents parking schemes are designed to make the most out of a scarce resource... space for parking in residential streets.
A parking permit allows free parking at all times, any day, in your zone. Restrictions apply fo non residents, see the signs in your street.
You are allowed up to three vehicles registered at the owners address, or confirmed as a company vehicle by their employer. Plus one visitor per address.
For details of the parking schemes in operation see your local District/Borough council.
The issue of a permit does not guarantee a parking space for the holder.