'Multiverses' generally require a higher order dimensional environment than our four-dimensional universe.

We can only really illustrate it by using lower order dimensional examples though, as we can't directly show a higher dimensional order object in a lower order dimensional environment.

So draw two separate lines on a sheet of paper. Each one of these notionally one dimensional lines represents a four-dimensional universe. Now these one dimensional lines have been drawn on a two dimensional surface i.e. the sheet of paper, and what separates them is the second dimension of the sheet of paper, the one at right angles that gives it an area.

In a 'multiverse' then, numerous four-dimensional universes would be separated by a fifth dimension, one that our four-dimensional universe doesn't possess, just as the lines on the sheet of paper only have length, but no area.