The contents of the agreement will depend upon the parties involved, the relationship, and the issues that are being resolved. It must be specific about the particular claims that are being settled. A general catch all provision will not be sufficiently precise to be effective.
The agreement should cover the responsibilities of both parties to uphold the agreement. For example, it may state that you will make a specified payment and offer a positive reference while your employee will waive any employment claims and agree to keep the matter confidential.
It is helpful to include details of how the payment figure has been reached, as there may be tax implications arising because of the agreement.
If the agreement is being made to end the employment relationship, it should detail how this will be done. For example, will the employee work their notice, or will the relationship end immediately?