There are a lot of different clip less pedals on the market, the first were Look, the ski binding company went into the cycle business and now also manufacture frames, since then Shimano and Campagnolo have made similar systems for road, Shimano and Time are leading the way for mountain bike pedals, but there are many others to choose from.
Setting up your shoes
If you are replacing old worn shoe
plates, draw a line round the old ones before you take them off, then the new should be in the right place, but allow for a little bit of
difference as sometimes they are not quite the same. Keep the old bolt spacers, as you might need them one day, if you loose one or one has to be replaced.
Look style plates have three bolts and SPD style have two.
For new shoes it's a bit of trial and error, first you need to get the shoe plate in roughly the right position, this means the ball of your foot (the knuckle) has to be over the axle of the pedal, so that you are always pushing down through the stiffest strongest part of the pedal.
Next you don't want the inside of your shoe to be rubbing against the crank or do you want your feet wide apart,
so set the plate so the shoe that there is a little gap.
Lastly is the angle of your foot, this is different from person to person and from foot to foot, this is where you have to go out with a screw driver in your pocket and if it doesn't feel right you have to stop and move it a little here and there.
Usually first impressions are correct, as soon as you jump on the bike if it doesn't feel right it probably isn't.
Some riders are always moving this and that, but if a shoe plate is not right it can cause a lot of problems with knees, ankles, hips and eventually your back if you whole posture is out of place, so it is very important to get this right to start with.
Adjusting your pedals

Once you have got the shoe plates in the correct position that's all the hard work done, the pedals themselves don't need much work.
There are tension adjusters on all pedals and you need enough tension to hold the shoe plates into the pedals, but loose enough so you can get your foot out when you stop.
Which ever foot you put down first you'll probably have the tension slightly looser than the other.
How to look after your shoe plates and pedals

Keep your pedals clean and well oiled, spray them with oil to keep the clip and spring nice and smooth.
Also check that the plates and the pedals are not worn or have any small stones stuck in them as this can cause bad clipping in and out and can cause a lot of problems with the position of your shoe on the pedal and can give you a leg muscle injury.
If you get squeaky plates a little oil should sort it out.