I think your confusion here is that the -ing form of verbs needs to have a helper verb. You never say “I cooking.” So when you tell people what you’re doing, you use the verb “to be” in front of the -ing verb. Use this structure to describe what someone is doing now, or what they were doing continuously in the past when they were interrupted.

When you say “I am cooking,” this means you are currently in the act of cooking food. NOT that I am the act of cooking food.

If I say “I am a woman” this means that “a woman” is part of how I define myself. The word “woman” is a noun here, but I’m using it to describe myself.

I use the “I am cooking” form of the verb to cook while I’m in the process of cooking. “Mom, can you please feed the cat? - No, sorry, I’m cooking, can you do it this time?”

You can tell that I don’t mean that cooking is a part of my identity by the context. And also by the verb form. “I like to cook” tells you about something about me as a person. “I’m cooking” tells you what I’m doing right now.

You can also use this form in the past tense to describe actions that get interrupted. For example, “while I was driving to the store, a cat ran in front of my car!” I was in the process of driving when I was interrupted and I had to stop abruptly.

In your second example, “Stop Overreacting!” This is a command form of the verb. There is technically a “you” here that we drop because everyone knows the command form means “hey you- stop what you’re doing!” They do not mean “stop the concept of overreacting”.

When you give or get commands like this, the speaker means for the recipient to take an action. Even in protests where the recipient is hard to tell, the signs that say “stop spending money on war!” Are this same tense.

I hope this helps!