When it comes to race... there is the human race. The end.

The concept of race is not a real human characteristic and is not recognized as valid by biologists. It is an arbitrary and invented division where none actually exists. The race concept breaks down because there is as much natural variation WITHIN a so-called racial group as there is BETWEEN so-called racial groups. For example there are "white" people who have many of the same phenotypic traits shared by "black" people, and vice-versa.

Since there is no such thing as race we cannot use that idea to describe ethnicity. That means ethnicity must be a (mostly) cultural phenomenon. Ethnicity may be defined by elements such as language, food/cuisine, music, religious tradition, mode of dress, ethics, values or morals, and even legal system. For instance, one could argue that graft is endemic in certain cultures largely as a result of the laws instituted by imperialist rulers like Napoleon, who told his tax collectors to collect their own salaries while they were at it. In other words, graft was institutionalized. Someone growing up in that system learns to accept what others would call "corruption" as simply a normal way of doing business. That system would exist in a given geographic region with a certain language or mix of languages, a dominant religious tradition, and distinctive cuisine and music. The local environmental conditions would tend to favor certain phenotypes (say, darker skin if you are located closer to the equator) but the peripatetic, migratory, explorer nature of humans would always ensure some degree of mixing with outside groups. Put it all together and you have an ethnicity.

there is no such physical thing as race; there are populations and families but race is a social construct. race, as i perceive it, is something put on a group from outside and ethnicity is something a group puts on itself from inside.

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Neither until it comes up. Been kinda lucky.

I mostly just think about culture: what language does this person speak? Can we understand each other? What kind of values are they likely to have? Are there any serious, obvious barriers to our ability to get along? What do they consider respectful, rude? How should I conduct myself, for maximum peace, goodwill, and benefit?

If I happen to know something about the culture ahead of time, then great: I've got a set of presets I can (carefully, without sliding into assumptions) work from. Japanese? Okay, probably values collectivism over individualism, probably very big on respect, deference, and saving face. I should take off my shoes in the house, and bow a lot. Ethiopian? No clue. Eyes open, head on a swivel, best behavior.

How a person looks or what part of the world they come from may give me some shortcuts to the kind of understandings I want, but they're not ends in themselves to me. Skin color and costume don't determine how a person thinks and behaves--so I regard them as the potentially-useful markers they are, and press on toward the important stuff.

'The History of White People' by Painter, 'Stamped From The Beginning; The Definitive History of Racist Ideas in America' by Kendi and 'How The Irish Became White' by Ignatiev are all great books explaining the lie that is race. I think the first one is the best. As @A2Jennifer said race as a powerful overarching social construct does exist but, just like gender, it is a myth. Because of this I try to walk that line between taking into account our encultured race and realizing it's based on a lie.

I suppose "ethnicity" is just a more polite term than "race". But whatever word you use, it has more to do with your empathy for fellow beings than any technical definition.

There is no basis for race in science. As for culture I consider it behavior among populations. The best thing about different cultures is the food. ?

They are both sometimes used interchangeably, but IMO race is person's physical characteristics, where ethnicity would be social and cultural groups you belong too. Mayans and Aztec would be different ethnicities. Hutu and Tutsi are also ethnicities. Both are of the same race. But I'm no sociologist, or whatever-ologist is an expert in such topics.

[diffen.com]

Race isn’t a biological fact but a social construct. That doesn’t mean that it’s impact isn’t real.
I do research and program work in an urban Native American setting and there is a focus on cultural competency/humility. It’s important to be aware of how race and ethnicity and culture may effect people without assuming that you know who individuals are based on those characteristics.

What do you mean, think in terms of race and ethnicity? A race of people is a population that shares common physical traits and ethnicity is a population of people that share a culture. Some races, some ethnicities are discriminated against and marginalized. That is how I think in those terms.

I try not to think in terms of race, since it's basically a meaningless term which just groups together people with practically minor physical differences. As far as ethnicity, isn't that just another word for culture? It seems to me to be.