Plain version: a representation is what the applicant tells the insurer to get the policy, such as answers on the application or statements to the underwriter. It is said to the insurer, not written into the policy as a promise.
Basic rules:
It may be oral or written (§350).
It may be made at the time of, or before, issuance of the policy (§351).
It is presumed to refer to the time the contract is completed (§356).
When is it false? Section 358: a representation is false when the facts fail to correspond with its assertions or stipulations. Intent is not part of the test, so an honest mistake can still be a false representation.
What it can and cannot change:
Section 354: a representation cannot qualify an express provision of the policy, but it may qualify an implied warranty.
Section 355: a representation may be altered or withdrawn before the insurance is effected, but not afterward.
The effect: if a representation is false in a material point, the insurer has the right to rescind the contract (§359).