When you first get your period it will be irregular for several years. Until your hormones level off and you get through puberty, it will be hard to track when it will come because it won't always be on schedule. You may go months without a period and then have one all the sudden. It's hard to know when it will level off.
But the way used to track it is that I would draw a star symbol in my calendar on the first day of my period and a star every day that I had it. Once your period gets more regular it should come approximately every 28-32 days after the first day of bleeding. So you'd count 28-32 days after your first star to determine the approximate date of your next period. But again, since you just started, it may not always be on time or come at all for a month or more and that's normal so don't panic if/when that happens.
Not all periods are alike but u can track it on a calendar. My period didn't always Coe the same time every month but it came every month. And I tracked ot. When it is heavy u will know and when it starts to get light u will know there will be a difference in how much blood u get in a pad
There are also several helpful apps out there! For example I am viewing this forum through the My Cycles app. It is discreet and easy to keep track.