Different parts of the trains
I am sure that you are used to the idea of a train being divided into first and second class seating and into smoking and non-somking areas but Deutsche Bahn has a few more ideas to keep you on your toes.
Most trains have a zone for disabled people. This will include seats with extra legroom, spaces for a wheelchair and seats for those accompanying a disabled passenger. They will also be located close to a disabled toilet which also doubles up as a baby changing room. Feel free to lounge out in the disabled seats and dump your luggage all over the wheelchair space - loads of ignorant folks do - but don't be surprised to be told to move on by the train staff if somebody wanders up on crutches.
Some of the newer trains have areas for small children. You can reserve places in those if you are travelling with kids and they are handy as they generally have room for the kids to play.
Newer trains also have quiet zones and mobile phone zones. The mobile phone zones have repeaters so that you have a better chance of getting a signal. The zones with a repeater are marked with a picture of a cellphone. The quiet zones either have a picture of a cellphone with a red line drawn through it or a profile of a face with a finger pressed to its lips. In the quiet zone, you should not use a mobile and you should not hold conversations. If you do, the other passengers may ask you to shut up and the train staff will back them up.
A tiny number of trains have WLAN hotspots but they rarely work and even if you can connect to a server, it is unlikely that you will be able to reach the internet. If you do, you will need to pay for the privilege. One pitfall to consider is this: you get on the train, turn on your laptop and discover that there is a hotspot and it asks you for a credit card payment for an hour's use. You pay and start to check your email but then the train leaves the station and you discover that you have just paid for an hour's time on the hotspot in the station cafe.
Many long distance trains have power outlets for notebooks. They might be available for just a few seats in one or two carriages but newer trains have an outlet for each pair of seats. If you choose to sit by an outlet on a train with but a few, don't be surprised if someody wants to plug his laptop in and leave the power lead trailing across your knees. If you don't like the idea, don't sit next to the only free outlet if you don't intend to use it. If you have an older laptop or one that has a high power requirement, you might find that you cannot use the outlets as you trip the breakers. Older trains actually have a manual reset switch for the breakers which is handy if your machine only occasionally causes trips. Other trains have breakers that can only be reset by the train staff.
Finally, there are the Bahn Comfort areas. Bahn Comfort is Deutsche Bahn's frequent traveller program. Bahn Comfort seating areas are indicated by small signs bearing the words Bahn Comfort. The seats in the Bahn Comfort areas are reserved for people with Bahn Comfort status. You can sit there anyway but, if you choose to do so, you will have to give up the seat to anyone who comes up and flashes their Bahn Comfort card at you.
When you are the station, you will find posters on the platforms which indicate the location of these parts for all of the trains that will use the platform.