Complaints/Cause of Action/Lawsuit:

You have been injured; you suffered some sort of loss.  Someone did something to you and you feel "they need to pay".  A complaint is when you file papers with the court to identify what somebody did to hurt you and why you feel they need to pay.  The court determines if they caused your injury and have to pay.  So when you are filing a complaint, write it like a story if you do not have a lawyer, and sometimes, the more details you provide, the better off you are.  Be precise.  For example, I paid him to cut my lawn, and instead, he never came to do the job; or, he cut the lawn and broke the window to my van.  With dates, times, and as much details, and proof, like a contract, to show what you are complaining about and why he/she needs to "pay".  

The court clerks can help you decide at times where your complaint needs to be filed.  There are many types of courts.  Drug Court, Family Court, Supreme Court, Child Support Court, Superior Court, Traffic Court, and Small Claims Court, etc.  So, make sure you are filing your action/complaint in the right court.  Otherwise you are wasting your time because the judge or the opposing side will quickly let you know you are in the WRONG COURT.