C++: What are the differences between using "const" or not?

Question

I learnt from this app that "const" is to make constant numbers or strings or something else.
But when I was doing some practice on operator overloading on my own, some errors occurred if I didn't use "const" with parameters in the operator overloading function. (Sorry for poor english)

#include <iostream>
#include <string>

class sample {
int data;
std::string word;
public:
sample(){}
sample(int a, const char b[]):data(++a),word(b){}
sample operator+(sample& s) {
sample d;
d.word = this->word + s.word;
return d;
}

};

int main()
{
sample me(1, "I am learning C++");
}

In the above case, (In line 9 of the code) if I use "char b[]" instead of "const char b[]", some errors occurred. Why?

Answer 1

Oh....thx~

Answer 2

so const* char represent a string type?🤔