Use "SceneManager.LoadScene()" to Load Another Scene via Scripting: https://docs.unity3d.com/ScriptReference/SceneManagement.SceneManager.LoadScene.html
Multiscene Editing: https://docs.unity3d.com/Manual/MultiSceneEditing.html
Recommended Tutorials:
HOW TO CHANGE SCENES WITH A TRIGGER IN C# UNITY TUTORIAL: https://www.youtube.com/watch?v=9lPCv9kkbSI
How to make AWESOME Scene Transitions in Unity!: https://www.youtube.com/watch?v=CE9VOZivb3I&t=4s