Outlets not working in trailer

Thank you all. I am beyond a novice and tried to look up some of your terms. So, no, I didn't know you had to be plugged into a shore line,,duh,, I thought the 12v batt would be sufficient. And, no it doesn't appear by the nice schematic Old Biscuit posted, that there is an inverter. There was a very large 3-prong adapter. Easy enough to plug it in, but it appears that I need an extension cord with 'spread apart' prongs to plug into this thing. Many of you have said to just plug a household cord into the trailer, but honestly, I cannot find where to plug a shore line into. Also, is the large plug I found a converter... I looked it up and several different photos show up, including some that look like the adapter i found. Thank you all so much again! Sorry for the delay,, work has firewalls on all our computers and has you blocked.