Glossary

Flapperons: (c) Tonyo from Ezone. Are a way of altering wing camber to change the lift characteristics of the wing section. For example, lowering both ailerons by around 5 degs. from neutral will provide considerably more lift, allowing you to fly slower and/or carry higher weight, and (in a slope soarer) allow you to fly in lighter winds. 

Spoilers: (c) Tonyo from Ezone. Destroy the lift of the wing where they are used and give a higher sink rate as the effective wing loading is increased. The effect on the glide is to steepen the glide angle with little increase in speed making landings a positive affair as there's little 'float' on rounding out for touchdown. They provide full control and avoid excessive speed building when diving out of lift or when approaching over obstacles. I prefer air-brakesas they are easier to use and set up.

Like most things, the angles needed on flaps depend on the model. Broad chord flaps need small amounts to make large differences. Even narrow chord flaps are fairly useless beyond 10 degs. Don't forget that flaps can also be used in reverse. Five degrees of up will speed up your model at the expense of some lift but will usually make it more stable at speed. This is where spoilers come in useful to get rid of the speed which you would find difficult to bleed off in the normal way.
I'm not sure at what point one becomes the other - in many ways they can be regarded as the same thing.

However - spoilers tend to be blades attached to the top, bottom, or both surfaces of the wing which can be raised to interfere directly with the layers of air passing close to the wing and providing lift. They disturb the air and destroy the lifting effect over that part of the wing. You get a very positive change if they cover 20% of the span . Size is around wing section thickness or slightly less. Location is usually just on or behind the highest point of the section, so the mainspar is a very handy support for them. . There is only slight trim change, and the effect is felt over the full speed range. At high speed they act as airbrakes as well. The simplest are hinged at the front and raised by a bellcrank system or torque rod. Commercial ones are more sophisticated (Graupner etc) and slide up and sideways so have less problem to overcome the aerodynamic loads.

Airbrakes: (c) Tonyo from Ezone. Can be any variety you can think of. Something to make a big resistance. A portion of the trailing edge, at the wing root, is my preferred type. - these are really terminal velocity brakes. You pop them out, stuff the nose down near vertical and they limit the max speed without over stressing anything. The rotation is set up so that about 1/3 is above and 2/3 below the wing. On a 130" soarer I have one each side 12" x1.75" - you can imagine the effect of 40+ sq in at right angles to the airflow! It's easy to land the model before the bungee parachute has returned to earth. Other types are flaps dropped to 90 deg.(sometimes combining with raising the ailerons to provide a variation of crow brakes); hinged canopy( at the front or, more effectively, at the back - make sure your radio and batteries are firmly held in!); Barn-door brakes from the fuz.; split rudder ; braking parachute - a once only system unless you can rewind it back again.

Some more suitable than others depending on the type of model.