How can I link one scene to another?

My game application has 3 levels: easy, average and difficult. After each level is finished, an option will be given for the user to move to the next level or stop the game. I created 3 scenes for each level. How can I call one scene from another?

you need to go in File-> BuildSettings. You need to add all of your scenes to the windows dragging them from the project panel.
Put them in order. The number is important.
Now let’s say you want to continue so you press C.

if(Input.GetKeyDown(KeyCode.C))Application.LoadLevel(numberOfTheLevel);

You can also use strings:

if(Input.GetKeyDown(KeyCode.C))Application.LoadLevel("NameOfTheLevel");

But my point of view is that you are more likely to do a typo mistake with strings than number. Personal.

you can look at this for more info: