Here is a sign from Haringey which caught out (by cctv - which won't happen soon) a gentleman who misunderstood and parked at 6.10pm because he only read the bottom panel.
In order to understand this sign (diagram 639.1B with optional panel 638.1), start at the top and work down:
On a Sunday you can park all day, free, as Sunday isn't mentioned at all.
Now let's talk about Monday through Saturday.
The top panel, the yellow one, has the "no parking" roundel so you cannot park in this bay from 8 to 9am or from 6 - 7pm (presumably to keep the road more clear for rush hour transport although Mr Mustard doubts it does any good as there isn't room along the whole road for 2 lanes. So far so simple for the average motorist.
If however, you are a delivery driver you cannot stop here, not even for a minute, to deliver or collect goods i.e. a parcel. The same goes if you are moving into a new flat and want to unload your possessions, you must avoid the two hours showing in the top panel.
The middle panel, the white one stops those short stops to deliver or collect. No exceptions, no differentiation between private or goods vehicles, do not stop for longer than it takes you to read the sign. Blue badge holders cannot park because it is a no loading bay for those two 1 hour slots. You can, however, drop someone off or pick them up (known as boarding and alighting, but don't take longer than it takes to do that safely and don't sit there for 2 minutes whilst the passenger comes out of a shop).
The bottom panel is fairly standard:
You can pay and park for 2 hours between 9am and 6pm.
You cannot return for 2 hours and if you do then you need to pay again.
You can drop off & pick up passengers (usual max is 2 mins but longer for elderly, young & disabled passengers who may need to be accompanied).
You can load and unload (usually up to 20 minutes for goods vehicles).
Blue badge holders can park for free (except in Westminster, Kensington & Chelsea, the City and the most southerly part of Camden where payment has to be made and an extra hour will be allowed - so if you only need an hour pay for the shortest possible increment of time) from 9am to 6pm.
From 7pm to 8am you can park for free.