From this page of the Returnal game guide you will learn how to stagger opponents to gain an advantage during the fight.
How to stagger an opponent?
The Stagger bar gets filled up when you shoot at the enemy. The bar is located under the enemy's health bar. If it fills up to 100% and starts to glow red, the enemy will be immobilized for a few seconds and will not be able to perform any actions, which will make it easier to finish them. Each weapon loads the stagger bar at a different pace. The most effective ones are shotguns and grenade launchers.
Aliens inhabiting particular biomes of Atropos have weak points, which are marked with a red square. Hitting these points increases the damage to a great extent and speeds up the process of stunning the enemy.
Stunning is especially useful when dealing with more difficult enemies who have significantly more health points than normal enemies.
How to increase stagger power?
Stagger power in the game Returnal can be increased with the special artifact known as the Unfed Pod. For each parasite attached to the suit, the stagger power will be increased by an impressive 20%.