UV Channel 1 is fine for Lightmaps, but Channel 0 is all over the place and overlapping. Which is to be expected if you didn’t unwrap it at all.
You’re best of using a 3D modelling program for this sort of thing. You could auto-generate UVs for channel 0 in Unreal for now (I think) though.
UV maps are essentially taking a 3D mesh and visualizing it in 2D.
I’m sure you made cubes from “nets” in school. The net is essentially the UV map. Another way to see it is taking an animal and skinning it to make a rug.
Net example HERE