Silly question perhaps but I'm a bit puzzled. The bed has a mattress, mattress pad, sheet 1, sheet 2, a thin white blanket, sheet 3, duvet with a removable cover and some more decorative stuff.
In Germany you would sleep between sheet 1 and the duvet and the other layers wouldn't exist. The sheet and the duvet cover would be changed regularly.
What about the American bed? Where are you supposed to put yourself in and which layers are subject to be changed ?
You put yourself between Sheet 1 and Sheet 2.
All the other layers on top are meant for warmth. It being summer, you may not need them all - feel free to remove any layers you don't want, and put them on a chair or in the closet. (Pro tip: if you want a little more air flow, untuck Sheet 2 from the mattress.) If somehow you're too cold, there are usually extra blankets in your closet. The staff will make the bed each day, reassembling all the layers in their original formation.
You can expect that Sheets 1 and 2 were clean upon your arrival. Once upon a time, hotels would change them every day during your stay. For "environmental reasons" (and also to save money), it is now more like every 3 days, but you can usually get them changed more often upon request. (Sometimes the hotel will give you a little sign you can place on the bed to request clean sheets.) At "extended stay" properties (eg Residence Inn), they may only be changed once a week during your stay.
The same policy probably applies to Sheet 3 and the duvet cover, but I am not certain; these layers are not always present. As to the other layers, they are typically changed less often. I don't know what the industry standard is, but you can always ask the staff if it's important to you (dial 0 on your room phone). So it would be courteous of you to try to keep them clean.
You have found yourself a fancy bed. At cheaper hotels and motels, you usually just have: mattress, mattress pad, sheet 1, sheet 2, wool or synthetic blanket (plain color), patterned quilt or bedspread.
I travel a lot, and here's how I handle it.
Unless you are staying in a hotel that washes the comforter/duvet between each guest, you should immediately pull it off the bed and throw it on the floor1. Then wash your hands, because god only knows what was on that duvet.
Look in the closet for a plastic bag containing a spare fleece blanket. If it is in a plastic bag, it is more likely to be clean than the duvet/comforter was.
Get in bed, between the sheet covering the mattress and the sheet above it.
1 I also have a special treatment for the remote control. If I have Purell handy, I douse the remote control with it. If I don't have Purell, I take the clear plastic bag in the ice bucket, put the remote control inside the bag, and wash my hands. This is especially important if your hotel offers adult movies on demand, because if those movies are available, you can bet your life that an enormous number of people have used the remote to choose an adult movie, then masturbated, then used the remote to turn the movie off. Gross.
It's a good idea to avoid walking in bare feet in a hotel room, unless you like athlete's foot and/or jock itch.
