First Information Report (FIR)

A first information report ( FIR) is a written document prepared by the police when they take information about the commission of a cognizable offence. It's a report of information that reaches the police for the first in point time, which is why it's called the First Information Report. It's generally a complaint lodged with the police by the victim of a cognizable offence or by someone on his/ her behalf.

Anyone can report the commission of a cognizable offence orally or in writing to the police. Indeed mobile phone communication can be treated as an FIR. It actually fills up from, a complaint lodged with the police by the victim of a cognisable offence. And someone on their behalf. Someone can make such a report either orally or write to the police, so it's necessary to know about cognisable offences. These are serious felonious offences that pose an immediate peril to society similar to murder, rape, or thievery. For a non-cognisable offence, an entry in a community service register or in the station journal is made.
Each FIR is necessary as it sets the process of felonious justice in a stir. Police can take a decision after registering an FIR. Anyone who knows about a cognisable offence, including police officers, can file an FIR.

The plaintiff or supplier of the information has a right to demand that the information recorded by the police be read to them. Once the police have recorded the information, it must be signed by the person giving the information. The plaintiff can get a free dupe of an FIR. The date, time, place, incident details, and description of the person( s) involved must be included on FIR.

FIR according to CrPC (Code of Criminal Procedure, 1898): 
According to section 154 of CrPC, in the title Information in cognizable cases: 

Every information relating to the commission of a cognizable offence if given orally to an officer in charge of a police-station, shall be reduced to writing by him or under his direction, and be read over to the informant; and every such information, whether given in writing or reduced to writing as aforesaid, shall be signed by the person giving it, and the substance thereof shall be entered in a book to be kept by such officer in such form as the Government may prescribe in this behalf.

Cognisable Offence:
According to Wikipedia: Generally, cognisable offence means an offence in which a police officer has the authority to make an arrest without a warrant and to start an investigation with or without the permission of a court. By contrast, in the case of a non-cognisable offence, a police officer does not have the authority to make an arrest without a warrant and an investigation cannot be initiated without a court order. The police can file a first information report (FIR) only for cognisable offences. In cognizable cases police can make an investigation without prior permission of a magistrate. Cognizable cases are more serious than non-cognizable cases. Normally, serious offences are defined as cognizable and usually carry a sentence of 3 years or more.
According to CrPC (Code of Criminal Procedure, 1898) Section 4(f)
Cognisable offence means an offence for, and "cognizable case" means a case in, which a Police-officer, may, in accordance with the second schedule or under any law for the time being in force, arrest without warrant.

Non-Cognisable Offence:
According to CrPC (Code of Criminal Procedure, 1898) Section 4(n)

"non-cognizable offence" means an offence for, and "non-cognizable case" means a case in, which a police-officer, may not arrest without warrant.

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