With a settlement agreement, previously know as a compromise agreement, you waive your rights to raise employment-related claims against your employer. Such an agreement can be entered into at any time during your employment but is usually entered into at the end of an employment period.
Settlement agreements are entirely voluntary; you should not allow yourself to be bullied or forced into waiving your rights. If you are not satisfied with the package offered to you in exchange for waiving your rights, or if you have been promised something that is not in the agreement, you should ask your employer for the relevant changes to be made.
Independent legal advisers will be able to highlight to you any unusual provisions in a proposed settlement agreement and can negotiate changes to the agreement on your behalf.