If you plan, for example, to go from Amsterdam to Utrecht by train, you can buy a 'day return' for that. They are available from NS ticket machines and NS service counters.
You can also buy them online, but payment is only possible with the 'Ideal' method, which implies you have a Dutch bank account. Credit cards are not accepted.
You might, however, ask someone you know at your destination, to buy a ticket for you. The ticket comes as a pdf-file by email. You have to print it before entering the train.
You need to choose the route, and also the date of your trip. They also ask your name and date of birth.
Once bought, you can not change the destination, or date, or ask for a refund.
Train passing train crossing