I wonder about a particle's energy when mass is obtained or lost

[seonjunyoo]

According to Einstein's formula, energy is generated when mass is obtained or lost.

What does losing or gaining mass mean for an atom or particle valence?
It's simply because of the formula I don't want this kind of answer
I want. What does it mean for an atom or particle to lose or gain mass from the perspective of an atom or particle?

Along with What does mass mean for an atom or particle?
If you don't understand the question, I'm sorry. My English is not my first language

 

[mfb]

The energy is not generated, it is just converted from one type to another.

What does it mean for an atom or particle to lose or gain mass from the perspective of an atom or particle?

The mass changes. What is unclear?

As an example, a hydrogen atom has a slightly smaller mass than the sum of a proton mass plus an electron mass.

 

[berkeman]

According to Einstein's formula, energy is generated when mass is obtained or lost.

I don't know if this is what you are referring to, but are you familiar with Nuclear Binding Energy?

https://en.wikipedia.org/wiki/Nuclear_binding_energy