The .map() function will go through the entire array, and on each step of that process it will take the current item that we are looking at and will pass it as a parameter into the function. You can then do whatever you want to that item, and whatever you return from your function will replace what is in that position in the array.

Say for example, with the array you gave in your question, we wanted to remove the name and last_name properties, and combine them into a full_name property. We can do the following:

 let people = [
   {
     id: 1,
     name: 'jhon',
     last_name: 'wilson'
   },
   {
     id: 2,
     name: 'maria',
     last_name: 'anyway'
   },
     id: 3,
     name: 'lastOne',
     last_name: 'example'
   }
];

people = people.map((person) => {
  return {
    id: person.id,
    full_name: `${person.name} ${person.last_name}`
  }
});

After this code runs, our people array would look like this:

[
   {
     id: 1,
     full_name: 'jhon wilson'
   },
   {
     id: 2,
     full_name: 'maria anyway'
   },
     id: 3,
     name: 'lastOne example'
   }
];

You can think of it as doing something very similar to this:

function transformPerson(person) {
  return {
    id: person.id,
    full_name: `${person.name} ${person.last_name}`
  }
}

let newPeople = [];
for (let i = 0; i < people.length; i++) {
  newPeople[i] = transformPerson(people[i])
}

people = newPeople;