Beginners Question (Expressions are not allowed at the top level)

Executable statements, such as TextLabel1.setLabel(inputText: "Hello World") are not allowed to be placed on the top level, as the error message is saying.

Such statements needs to be in a function or some closure.

Code Block 
import Foundation
let textLabel1 = ViewController()
func mySetLabel() {
	textLabel1.setLabel(inputText: "Hello World")		 //<- This is not at the top level
}

This will compile, but may not run as you expect.

---

how can I call this function?

It depends on when you want to call the function.

In this code, you don't need to initialise name (with the label).

Code Block 
		@IBAction func pushedResetButton(_ sender: Any) {
				var name = textLabel.stringValue
				name = "Button Reset is pushed"
				textLabel.stringValue = name
	}

Could have just

Code Block 
		@IBAction func pushedResetButton(_ sender: Any) {
				textLabel.stringValue = "Button Reset is pushed"
	}

Here is an example on how to call the func:

Code Block 
		@IBAction func pushedResetButton(_ sender: Any) {
				setLabel(inputText: "Button Reset is pushed")
	}

Several comments on your initial question

Code Block 
	import Foundation
	let TextLabel1 = ViewController()
	TextLabel1.setLabel(inputText: "Hello World")		 // gives Expressions are not allowed at the top level

You cannot set a value outside of a class or func.
What you do usually is to declare:

Code Block 
    var textLabel1 : ViewController! //	or textLabel1  : ViewController?

Then, set its value in a viewDidload

Code Block 
textLabel1 = ViewController()

Now, you can call

Code Block 
textLabel1.setLabel(inputText: "Hello World")

Your ViewController has outlets, don't initialise this way, but instantiate from storyboard.
How do you go to textLabel1 ? Through a segue link ?

Note:
TextLabel1 is not a class but a var. Should start with lowercase.
Name a ViewController as textLabel may not be the best choice.

Thank you for answering.
As in the first answer (from @claude31) I uderstand it is not possible to change a value that is inside a class.
So does this also mean I need to do all the logic within the ViewController class?

From the second answer (from @OOPer) I can see that I can get rid of the "Top level expression not allowed" message.
But as soon as you try to call the function, you have the same problem again.
So here again that all the logic needs to be done within the ViewController class?

Just before I try out some things, is it possible for example to call a function outside de ViewController class, that returns value?
That value will then be used inside the ViewCntroller class to change the label.
There is no direct way by changing the label. Or is there? I mean, there is no direct way to say "let label="text""?

So here again that all the logic needs to be done within the ViewController class? 

As I have already said, you need clarify when you want to call your logic.
For example, if you want to do something a little before a view controller is shown, viewDidLoad() in the ViewController class would be the right place.