It sounds like they are Auxiliary Lenses that screw into the filter thread of your kit lens. They were designed to be used on P&S cameras that don't have interchangeable lenses. They are usually very cheap, more so when compared to an actual interchangeable lens and optically very poor. Image Quality will be significantly compromised. In addition, Nikon lenses, especially the kit lenses were never designed to be used with these converters and the added mass at the end of the lens can actually damage the lens barrel that won't be covered by the warranty. The risk to your equipment more than outweighs the reward.
Made Decades ago, the Vivitar Series 1 lenses (Manual focus) with AI and AIS Nikon F mounts can be used on the D3100 though only in full Manual exposure mode without metering. Good Luck and Enjoy your Nikons!