Are you talking about the instance / class (
c) toggle on the New Class or Member pane?
That is used to indicate whether a routine should be a class (“static” in C++) member or an instance member of an object.
What you type in the New Class or Member pane (or just the “New” pane for short) specifies what type of new language construct that you want to create: subclass, routine (constructor, destructor, conversion method, method, coroutine), or data member.
The hint text should help you remember what syntax is expected for the different types of things you can create:
[Class.] SubClass | _coroutine | method[?] | ![constructor] | !!(destructor) | ConvertClass | @instance_data[?] | @@class_data[?]
Once you are familiar with the possibilities, the New pane is quick and easy to use - of course that is after you are familiar with it.
We recommend reading through the New Class or Member pane doc page in its entirety at least once. You might not remember it all the first time though you might have a fuzzy recollection that would remind you to look up specifics again in the future as needed.