References:

Unity Scripting Reference
Google
C# on Wikipedia
Unity Project Structure

Example of Unity C# file:

using UnityEngine;
using System.Collections;
 
public class ExampleScript : MonoBehaviour
{
    #region Fields
 
    // Public (visible in inspector and other script)
    public int myInt = 1; // Default: 1
    public GameObject myGameObject;
 
    // Internal (not visible in inspector, but visible to other scripts)
    internal int myInternalInt;
 
    // Private (only visible in this script)
    private float myPrivateFloat = 0.5f; // Default: 0.5
 
    #endregion
 
    #region Methods
 
    #region Initialization
    // Use this for initialization
    void Start()
    {
        // This is called when a GameObject, with this script attatched, is created.
        myInternalInt = -1;
        string s = "GO";
        Initialize(s);
    }
 
    /// <summary>
    /// Prints a string to the console. (Commenting your methods is awesome!)
    /// </summary>
    /// <param name="s">String to print. (Commenting your parameters is EPIC!)</param>
    private void Initialize(string s)
    {
        Debug.Log(s); // Prints the string to console
    }
 
    #endregion
 
    #region Update
    // Update is called once per frame
    void Update()
    {
 
    }
 
    // FixedUpdate should be used instead of Update when dealing with Rigidbody.
    void FixedUpdate()
    {
 
    }
    #endregion
 
    #region Triggers
    void OnCollisionEnter(Collision collision)
    {
        // This is called when this object's collider collides with another collider.
    }
    #endregion
 
    #endregion
}