Can the smart people of SW explain to me "e = mc squared"? Specifically,

I know that it is Einstein's famous formula and means "energy equals mass times the square of the speed of light". What I don't get is how the measurement works. Mass is measured in units of weight, right? Speed, in units of time and distance. How is energy measured by this method? Like, if we're doing metric, let's say you have a mass of one kilogram, and the speed of light is 299,792,458 metres per second. Square that and you get 89,875,517, 873,681,764 kilometres per second... or is it square kilometres per square second?? And then your energy outcome is 89,875,517, 873,681,764 kilograms-kilometres-seconds?? What does that even mean, other than "really really big"? I am sure there are many SWeeps here in the sciences who actually understand it so please explain it to me and the rest of us who dropped math and science after high school. Thank you!