About std::map in c++

AtCoder Beginner Contest 008

Problem Statements

An organization held an election to select a leader.The organization consists of N members, each with the most appropriate leader's name.
The leader will be chosen by the person who gets the most votes.Print the name of the person with the most votes.If you have more than one person who gets the most votes, you can print any name.

Enter

Inputs are given from standard input in the following format:

N
S1
S2
:
SN

An integer N(1 NN 5050) representing the number of members of the organization is given to the first line
• .
<li> Lines 2 to N represent voting contents of each member.A character string Si is written on the i(1 ii )N)th line out of the N lines.Si represents the voting content of the i-th person.
Si consists of only lowercase half-width letters and is between 1 and 50 characters long.

Output

Print the name of the person with the most votes.If there are a plurality of persons with the largest number of votes, any name may be outputted.Put a new line at the end of the output as well.

I have a question about the following answer code using std::map of the above question.

#include<bits/stdc++.h>
using namespace std;

int main() {
    int N, max = 0;
    string S,ans;
    map<string, int>m;
    cin>>N;
    for (inti=0;i<N;i++) 
    {
        cin>>S;
        m[S]++;
        if(max<m[S]){
            max = m[S];
            an=S;
        }
    }
    cout<ans<<endl;
    return 0;
}

I understand what m[S]++ means in the code, but I can't explain exactly.
Input e.g.

4
taro
Jiro Corporation
taro
saburo

As a behavior when it comes to

I understand that m[S]++ means m[S]=m[S]+1, so could you tell me how it works?Thank you for your cooperation.