Answer: Do they look like the silver things in the picture below? If so, those are brake cable end caps.
Question: What are they for?
Answer: They are for capping the end of brake cables. The brake cables on your Prevelo bike should already be capped. These are extras.
Question: Why did I receive extra brake cable end caps?
Answer: Bikes often ship with extra brake cable end caps so bike shops can adjust the brake cable length before handing a bike to a customer. However, when you buy a Prevelo, we adjust the brake cable length at our shop in Southern California before shipping the bike. So these caps are extra - call it a bike industry tradition.
Question: What should I do with them?
Answer: You can save them in case you ever lose a brake cable end cap. But honestly, that's pretty unusual and you will probably never use them. If you have really really really skinny fingers you can things them as thimbles. Don't be afraid to get creative.