[Quiz game] How do I make players contribute with questions?

Hello guys, I’m doing a quiz game but I want to make players contribute to the game with questions.
Any ideas of an easy and practical way of doing it?

Where and how to store and retrieve new questions?

I would do it like this:

Crate a new class “Question”:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

[System.Serializable]
public class Question {

	public string questionText = "What currency does the United States use as of 2015?";
        public List<string> answers = new List<string>() {"Dollar", "U.S. Dollar", "USD", "US Dollar"};


}

I use a list for the answer string so more than one answer can be correct if I wish.

Then, create a questionaire: Simply a list of the Question class:

public List<Question> questionaire = new List<Question>();

Now you can let players Add questions simply by adding to the list and filling in the values for questionText and answers.

To draw a random question:

string newQuestion = questionaire[Random.Range(0, questionaire.Count - 1)];

string questionTextCur = newQuestion.questionText;

To check if an answer is correct:

string answerText = "Euro";

if(newQuestion.answers.Contains(answerText)) {
     Debug.Log("Right answer!");
}
else {
     Debug.Log("Wrong answer!");
}

If by storing and retrieving you mean actually saving and loading to/from file, then look into Serialization and BinaryFormatters.