Compiler errors alle the time :(

Hi Guys,
I start to be a liitle bit frustrated as i receive very, very often "compiler errors". I try to learn Unity myself by using online trainigs that is why sometimes i rewrite the code from the tutorial. A lot of times i can't continue/progress because compiler errors appear even durin execution super simple scripts.

For example:
My script:

using UnityEngine;
using System.Collections;
public class ExampleClass : MonoBehaviour
{
void Update()
{
if (Input.GetKey("up"))
{
print("up arrow key is held down");
}
if (Input.GetKey("down"))
{
print("down arrow key is held down");
}
}
}

OUTCOME:
The referenced script (ruch) on this Behaviour is missing!
The referenced script on this Behaviour (Game Object 'Cube') is missing!
Assets\Scenes\ruch.cs(4,14): error CS0101: The namespace '<global namespace>' already contains a definition for 'ExampleClass'
ssets\Scenes\ruch.cs(6,10): error CS0111: Type 'ExampleClass' already defines a member called 'Update' with the same parameter types

Win32Exception: The system cannot find the file specified.
System.Diagnostics.Process.StartWithShellExecuteEx (System.Diagnostics.ProcessStartInfo startInfo) (at <9f8c4786222746238eb929db40bf8dd1>:0)
System.Diagnostics.Process.Start () (at <9f8c4786222746238eb929db40bf8dd1>:0)
(wrapper remoting-invoke-with-check) System.Diagnostics.Process.Start()
UnityEditor.DefaultExternalCodeEditor.OpenProject (System.String path, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/DefaultExternalCodeEditor.cs:131)
Unity.CodeEditor.CodeEditor.OpenProject (System.String path, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/CodeEditor.cs:31)
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)

 

Three things for starters:
- You can only have one ExampleClass in one namespace (if you don't use namespaces, then in your project)
- You always need to put your MonoBehaviours in a cs file with the same name as the class is, so ExampleClass always should be in a file named ExampleClass.cs
- if and when you post code on the forum, use the CODE tags, so it can be readable https://forum.unity.com/threads/using-code-tags-properly.143875/

Do this modifications and if you still have errors, please, post here again with the description of what's happening.