Section 1953 answers the question people ask when they are told "you signed it". Subdivision (a) makes void, as contrary to public policy, any provision of a residential lease by which the tenant agrees to modify or waive five categories of right: rights and remedies under § 1950.5 (the security deposit) or § 1954 (entry); the right to assert a cause of action against the landlord that may arise in the future; the right to a notice or hearing required by law; procedural rights in litigation about the tenancy; and the right to have the landlord exercise a duty of care to prevent personal injury or property damage where the law imposes that duty. These are void whether or not the tenant read them, negotiated them or initialled them.
Subdivision (b) deals with everything else. A clause waiving some other statutory right, not already void under subdivision (a) or under §§ 1942.1, 1942.5 or 1954, is void as contrary to public policy unless the lease was presented to the tenant before the tenant took actual possession. That is a timing rule with a practical edge: the addendum produced on move-in day, after the keys have changed hands, sits on the wrong side of it. Renewals are treated differently — the subdivision does not apply to a provision carried over from the lease being renewed.
Subdivision (c) limits the whole section to leases and rental agreements executed on or after 1 January 1976. Reading a clause and deciding whether it falls in subdivision (a), in subdivision (b) or outside the section entirely is exactly the kind of question to put to a lawyer with the lease in front of them.