At higher grades you must be able to discuss with the examiner musical features such as texture, form, style, and period of a piece of music. My own web pages to help with these parts of the test at Grade 5+ and at GCSE are available here!
There are always two pedals on a piano, sometimes three. They are used together or separately and in a variety of ways, vastly extending the range of timbres over the instrument. Learning to pedal also introduces another layer of complexity and challenge to your co-ordination skills, so can really only be taught face-to-face by a proficient teacher, but I hope these guidelines will be helpful.
The sustain pedal is used for legato pedalling and to add resonance and subtle overtones to the music
The una corda pedal weakens or softens the tone - by moving the hammers slightly 'off centre' on a grand, or slightly closer to the strings on an upright
Only comparatively modern grands have a sostenuto pedal
The most common mistake... 
...is to pedal with your feet, instead of
......... your ears! 
If you don't listen to the sounds you are making, it will be easy to play with too few changes of pedal. This blurs the sound too much.
If you don't listen, on the other hand, you may not notice that the pedal hasn't actually started working at all - many sustain pedals only fully engage when your foot is pressed quite low to the floor. As you become more proficient you will be able to use 'half-pedal' effects to your advantage....
If you listen hard, you will discover you can achieve subtle changes of tone with either the una corda or the sustain pedal, depending on how far you press down, which register you are playing in and so on.
To learn to pedal, it helps to know the mechanics of what you are doing. Take the piano apart and look at what is going on inside!
Play with the strings and dampers on view. Not only will you get a fantastic sound, you will also see how without the pedal, the dampers come onto the string to stop the vibrations when you take your finger off the key. With the sustain pedal pressed down, this doesn't happen, so the notes hold on for much longer.
Another common mistake...
...is to forget to keep your heel on the ground when you pedal. This is inefficient, uncomfortable and could do real harm. If you can't reach the floor, and you really must pedal, there is a gadget available to help you. Otherwise, best to wait, really work on your finger legato, and choose pieces for which pedalling is not essential, rather than risk damaging your posture and technique.
Legato pedalling
It is actually quite hard to co-ordinate feet and hands, especially as for normal legato pedalling they need to be slightly out of synch. Try just two chords at first (say C major and G7, or two triads built on consecutive white notes) and play only with your left hand. Once you can find them quite easily with your fingers, try putting the pedal down just after you play the first chord, and leaving it there while - quite slowly - you lift your hands away from the keyboard, prepare the next chord and then play it.
Your right foot will be going down once and staying down.
Your ears will notice the sound continues after you lift your hands
Your ears should notice the "smudge" when you change chords
Play it again, putting the pedal down just after you play the first chord, leaving it there while you move to the next chord, then lifting the foot and putting it down again before you lift your hands again.
Your right foot goes down once - then up and down once after the change of chord
Your ears should notice beautifully linked legato chords
Your ears should notice very little blurring of the two chords
When this is easy for you, try to add a third chord, and change the pedal each time.
Your foot will be going down - up - down - up, slightly "behind" your hands.
Your ears will need to work hard to detect those smudges, enjoy those beautiful legato chords, and educate those feet!
Resources
- Walter Carroll: Ripples or Shadows (from River and Rainbow)
- Burgmuller: Angelic Harmony (from Progressive Studies)
- Cyril Dalmaine: Evening Bells (from Queen's Highway)
