Are face shield okay to put on instead of face mask ?

They are different: A face mask filters out aerosols that may contain COVID and helps prevent them from entering your nose or mouth. A face shield prevents splatter and keeps aerosols out of your eyes... but it does not filter anything out. A mask with glasses is your best bet. Although masks can be uncomfortable, a ventilator and/or organ failure is far worse. Masks are really a small sacrifice to protect everyone.

Not really: If I were yo design a covid proper mask it would have an attached face shield since the stray virus could enter through your eyes. ( you can find some on the net.) A simple face shield can be added to a mask to increase effectiveness of your protection. It does not provide you or anyone around you protection from inhaled or exhaled viral particles or secretions.

No: Face shield is an adjunct to face mask protection, not the other way around. Best mask is N95 without valve, 3 stage surgical mask second, cloth mask is better than nothing.