The first thing to be aware of is the red and yellow line system. These lines run parallel to the curb (the edge of the pavement area by the road). A single yellow line means that parking restrictions are in place.
There will be a yellow plate nearby telling you the times this operates.
You cannot park during controlled hours however you can stop to let in or out a passenger but you should not leave the vehicle yourself. You cannot park, just stop for a short time frame while someone gets in or out. However it is normal that blue badge holders (disabled drivers) are allowed to park while displaying their badge.
Double yellow lines means parking restrictions are in force 24/7.
Red lines signify the road is part of a red route which means you cannot stop under any circumstances even to let a passenger out.
The hours of restriction will be shown on a red plate close by. Often these operate 24 hours in conjunction with a bus lane. Failure to comply with the restrictions will result in a penalty fine being issued. Red routes are also more strictly monitored and enforced than yellow lines.
Where parking is allowed on the street it's normally on a pay basis, either by a parking meter or pay and display machine.
Parking areas will marked by dotted white lines, they may be either one car sized (normal for parking meters) or a long section of spaces (normal for pay and display). You must be inside the white box area or you will be liable for a fine/penalty notice.
Parking meters accept only change and will not give out change. Change the hours that are charged for on the parking meter, apart from the restricted hours it will tell you the maximum amount of time you can stay parked for. You are not allowed to pay more after that time has elapsed to carry on parking, you must leave the space or chance a fine. While parking meters are allocated to single parking bays, pay and display machines covered a line of parking spaces. You pay at the machine and get a ticket with your expiry time. You must clearly display this in your car so it's visible to a parking attendant. Some area you will find are free to park on weekends or at least on Sundays while other areas will charge at all times.
Many residential areas will be restricted to parking for residents only and this is signified by a sign saying "Permit Holders Only", requiring the display of a special badge.
Many times your only real choice for parking will be in a public car park. These in London tend to be owned and run by NCP, National Car Parks. Not particularly cheap, expect to pay around £15- £40 for 24 hours in central London.
Parking regulations at one were time were exclusively policed by council employed traffic wardens. They were easy to spot with the distinctive black hats with a yellow line around it (which became the butt of many 'no parking' jokes).
While they still exist by the far the majority of traffic enforcement officers are now from private companies contracted by the local authorities.