there is / there are
Agreement after the expletive there.
After there, the verb agrees with the noun that follows. There is takes a singular: There is a crate on the dock. There are takes a plural: There are two crates on the dock. Do not use There is two crates.
Examples
Use There is a lock on the gate.
Use There are two locks on the gate.
Avoid There is two locks on the gate.