Part of Bullet Journalling is Indexing, usually it’s the first few pages of our bullet journal. It is a great way to keep track of important pages and collections for quick and easy reference.
It’s not usually the first page you start writing, but generally within a few days of starting your bullet journal, you will have page numbers to add to your Index. Try to keep up with it, doesn’t have to be when ever you add a fresh page, but it could be once a week or once a month. You’ll find especially once you start getting further on in your journal that it helps to find collections, and other important pages that you refer to quite often
There are several things to consider as well with Indexing. Do you bullet journal each day on a page, or each week on a page, or use both dailies and weeklies, depending on how you do it, you may want to group those pages together in your index to save on space, rather then indexing individual pages. I use a Monthly, as well as weekly spread, and dailies, and so I generally only index my monthly spread, as I bullet journal my weekly and dailies in my every day planner that I carry around, and I keep my bullet journal at home.
Depending on the journal that you use to bullet journal in you may have to create your own index, or remember to leave approx 4 pages (depending on how much you want to index). In the leuchtturm1917 dotted notebook which is the one that I bullet journal in, they come with indexing pages set out, as well all the pages are pre numbered for handy and quick indexing.