These connectors are needed to connect each section of LED Rope Light to its power supply. The 12vDC option has a 9v snap that connects to a battery supply, such as an 8AA battery cage or a 12v car battery. The House Current option plugs directly into an outlet. Once you have this Power Connector at the beginning of your Rope Lights, you can chain different colors end-to-end using the End2End Connectors (sold separately).
See our friend Howard's amazingly detailed soldering tutorial to learn how to work LED Rope Lights into your dream project: