When I booked my first solo trip to Seattle, I was honestly a bit overwhelmed by all the tabs and toggles on the Delta site. The best way to handle it as a beginner is to keep it simple: plug in your cities and dates, but don't rush the "Review" page.
I once accidentally booked a flight for the wrong month because I was clicking too fast! If you realize you need to change or modify your seat selection or baggage after the fact, it’s much easier to do through their mobile app. For immediate help, you can always reach out at 888-217-3324.