First select the language you comfortable in. i register account for myself so that I will be able to manage my bookings. A credit card is needed to be saved, this forms the verification that the train attendant would need from you to scan when they scan your tickets. Hence this credit card must be brought with you on your trip for the verification purpose. Very important to note this!
While doing the booking, must know very well which station you want to board from and alight at. If not familiar with the names, please research and double confirm before booking. Because similar names of station in a city/ country can mean different locations.
You can purchase a particular destination train ticket at Bahn.
or even their pass (eg. Bayern ticket) for a specific day for the number of people required.
the online ticket will be emailed but the words on it are mostly in german. definitely a website to book your train ticket when traveling in europe!