Install Gasket and Tighten Retaining Nut

What happens here

From underneath the sink, slide the rubber gasket over the strainer body, ensuring it sits flat against the bottom of the sink. Follow this with the paper or fiber friction washer (if included), and then thread on the retaining nut. Hand-tighten the nut as much as possible. Then, use pliers to tighten it further. As you tighten, excess putty will squeeze out from under the flange in the sink basin.

Goal: Secure the new strainer assembly from below.