Any category is a self referencing Tree model. So for creating a parent category, you just create a Category with that Name from the Category form.
And when you create new categories which should be children of the parent category, then select that earlier category in the Parent Category field and Save.
This will make the new category as Children of your Parent,
And if you want your parent to be at the highest level, make sure when you create such category, leave the Parent category field blank.
Perfect. Got it. Thanks for your prompt response Amit; appreciate it.