What does it do?
The point of an entire agreement clause is for it to be clear that the agreement does not include any terms not written down that might have been discussed during negotiations or that may have been included in past agreements between the parties or any subsequent representations made between them.
Real life example:
Abby purchases a car from a second hand lot cash. She asks all the questions she wants answers to and then agrees on a price and fills out the necessary paper work, including a sales agreement. Having signed the agreement she asks the sales representative whether the vehicle has a service plan included. The sales person says that it does. This representation is made after the conclusion of the agreement and is not recorded in writing between the parties. If the agreement has an entire agreement clause Abby will not likely succeed in trying to enforce the inclusion of a service plan.
Kleva Contract sample wording:
This Agreement is the whole agreement between the Parties. No terms or conditions not contained in this Agreement can be relied on.