Small Claims can only decide claims for money. The Small Claims judge cannot order a defendant to do anything other than pay a specific sum of money. Thus, you must be able to put a price tag on any damages you have suffered as a result of the defendant's actions.
Small Claims does not have jurisdiction in such actions as libel, slander, repossession or any other kinds of cases which do not involve actual monetary damages. If you have a dispute with your mechanic, for example you can base an action on you bills or the estimate cost of redoing his work.
However, you cannot ask the court to make the mechanic fix your car or release it before payment of a bill. Typical cases involve contact disputes, rental security deposits claims, accident damages, etc. Small Claims is also used by many merchants to sue consumers who have defaulted on loan agreements.