Is a written statement of truth made on oath to confirm the existence of certain facts, usually intended to be produced in court. An affidavit is therefore used as evidence of the person who authors it.
It is supposed to contain only what the author knows as actual facts.
A person who swears an affidavit i.e. provides the statements of truth, is called a deponent.
Lawyers normally draft affidavits basing on the testimony/witness/account of the deponents. The deponent sign the written statements after confirming the contents are true. The deponent, are limited to swearing to only matters that they can prove.
Second hand information is not allowed in affidavits. Do not lie in the affidavit. Affidavits are oaths of truth. A lie is perjury which is a criminal offence and is penalized by imprisonment of up to seven years.