What is the difference? Is one better than the other? How do you choose between the two?
Why does one not need to instantiate when calling a static method?

Well I can't conclusively say that one is better, because they serve different purposes.

Are you familiar with OOP? In OOP, static objects or members of a class that can be accessed directly from the class, while non-static members can only be accessed from the instance it belongs to.

C# follows a similar principle for the methods. The static methods can by accessed directly from the class, while non-static methods (or instance methods as I like to call them) have to be accessed from an instance. That is why instatiating needs to be done for instance methods, while for static methods it's just not needed, and furthermore impractical (see below).

In OOP, static variables are used for values which cannot be stored by an instance variable. Example: supposed you wanted to keep a count of how many instances of a class exists? How would you store that in a single instance?

The methods use a similar principle. They should be used for procedures for which it is impractical to do within an instance of a class. I tend to use them for broad procedures (not a technical term), meaning those that do not require me to instantiate an object. Example, adding two parameters. (This usage may or may not be correct, but I believe it is)

However, if you wanted to add two properties of an object, the method cannot be static, because as you would soon realize, static methods cannot access instance methods or variables within a class. Of course that makes sense because that static method would not know which instance of the class the get these from unless it were told, since it is not part of an instance itself)

For the sake of no further complicating things, I'll stop here. Let me know if you misunderstood anything.

static methods are used when you will need to access a method from many different classes or forms, you wouldn't want to create an object every time you needed that method. and you certainly wouldn't want to retype or copy and paste the same method into every class you needed it in.

an example would be the static method "Show" from the static class MessageBox.

when you need a messagebox, you just call a static method to show it. ex.

C# Syntax (Toggle Plain Text)

System.Windows.Forms.MessageBox.Show("some message");

System.Windows.Forms.MessageBox.Show("some message");

if it weren't static, you would first have to create an instance of the class that contains it it would be like

C# Syntax (Toggle Plain Text)

System.Windows.Forms.MessageBox MB = new System.Windows.Forms.MessageBox();
 
MB.Show("some Message");

System.Windows.Forms.MessageBox MB = new System.Windows.Forms.MessageBox(); MB.Show("some Message");

now wouldn't that suck?

it can have other purposes but that's the deciding factor for me.

when you need a messagebox, you just call a static method to show it. ex.

C# Syntax (Toggle Plain Text)

System.Windows.Forms.MessageBox.Show("some message");

System.Windows.Forms.MessageBox.Show("some message");