I often travel this way because my parents live in Amsterdam. The train station at Schiphol is one of the most convenient features of the airport. It’s right under the terminal, and it takes about five minutes to walk there from the terminal. If you’re not sure you can find it on your own, check out this guide to the airport:
https://amsterdam-ams-international-airport.com/en . Similar sites exist for many airports, and I always use them before my flights. The trip to Utrecht takes about thirty minutes with no transfers. You can buy tickets at the ticket machines in the station or in advance through the NS app. I recommend buying tickets in advance so you don’t have to stand in line with your luggage. Have you decided on your departure time from Utrecht yet?