Some themes requires that you fill a form field with a category ID. It may be easy to find a category ID if you’re an advanced WordPres user, but what about beginners? Here’s a very simple manner to find any category ID.
Once you’re logged in your WordPress dashboard, go to Manage and then in Categories.
Simply put your mouse cursor on the “edit” link related to the category you want to know the ID and look on your browser’s status bar: As you can see on the screenshot below, 1 is the id of the category.