The concept of the personal injury lawyer comes from "tort" law.  A tort is a civil offense, a legal wrong in which one party is injured because of the action (or inaction) of another person.  The injured party, called the plaintiff, sues the person thought to be at fault, the defendant.  If the plaintiff wins, the unsuccessful defendant is told by the court to pay damages, a certain sum of money. 
   Personal injury lawyers, also called PI lawyers, are attorneys who represent the injured party, the plaintiff.  Defense attorneys represent the person being sued, the defendant.  When one believes they have been injured at the hand of another and wants to seek money damages, one wants an injury lawyer. 
   Injury attorneys are typically paid differently from defense attorneys.  Defense attorneys are paid on an hourly basis, by the defendant or the defendant's insurance company. They are paid whether they win or lose.  Plaintiffs' attorneys usually work on a contingency fee basis.  That is,  they are paid a percentage of any settlement or jury verdict money.  Often the plaintiff will be required to pay some costs at the beginning of the lawsuit.  But for the most part, if there is no settlement or verdict, the plaintiffs' attorney is not paid.  If there is an award or settlement, the attorney will be paid costs plus a certain percentage.  The percentage may vary between 25% and 40% and often this amount is limited by state law. 
   The agreement  regarding the contingency fee should always bee agreed upon at the start of the case and it should be evidenced by a contract. 

Attorneys in California, like most states, are prohibited from soliciting employment (ambulance chasing).  Injury attorneys' advertisements are found in Phone Directories, TV and on billboards.  But this is not the best way to choose an attorney.  Sometimes an ad can be helpful if it contains information about the lawyer's background and practice.  Still,  you need an injury lawyer who fits certain criteria:  Certainly any attorney must be ethical and organized.  An injury lawyer needs to know trial law, and to have experience in the applicable area of trial law. 
     A certain amount of "specialization" takes place in injury law.  Some attorneys are particularly good at medical malpractice while others limit their practice to mass torts, aviation, travel law, etc. etc. 
     Better known injury lawyers will not take any case.  They will look for a case they believe they can win and one in which they can recover enough money to make the effort worthwhile.  Often, a prospective plaintiff visits lawyer after lawyer, "shopping" for someone who will take the case.  Lawyers these days are careful since they can do a massive amount of work on a case only to lose and make nothing. 
     It pays to do a little investigation and research before signing on with an injury lawyer.  For an essay with a few tips check this site.   And looking for a lawyer as soon as one knows of the injury is important since lawsuits must be filed within a certain amount of time or the right to a claim may be lost.