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.