There are several different types of trailer plugs: 50 amp, 30 amp and 15 amp. They all are different so that they only plug into the proper amperage receptacle.
Your trailer is set up for 30 amp shore power service. The first cord is made to connect from your trailer to a 30 amp outlet at campgrounds that have electric hookups. If you want to plug the 30 amp cord into your home electric receptacle, you need a second adapter which changes the 30 amp male plug to work in a 15 amp receptacle.
Keep in mind that you may not be able run everything in your trailer off a 15 amp home circuit. For instance, running the A/C and microwave together might take more than 15 amps, and could trip your home circuit breaker when the trailer tries to draw more than 15 amps.
