The namespace '' already contains a definition for 'GameManager'

Assets\Scripts\GameManager.cs(8,14): error CS0101: The namespace ‘’ already contains a definition for ‘GameManager’
Assets\Scripts\GameManager.cs(10,15): error CS0111: Type ‘GameManager’ already defines a member called ‘Awake’ with the same parameter types

You cannot have two classes with the exactly same name, here: two GameManager classes.