It is hard for us to understand. Is the universe infinite? Is it endless?
The concept of infinity is indeed nearly impossible for most human minds to grasp, for it is not a linear concept. Infinity extends in all directions, but infinity also has a pulsation to it. A pulsation of contraction and expansion, that is the nature of the universe within which you and Joshua reside. It is slow, very, very slow, in terms of your linear time, however there is seemingly an end which is the final contraction, and there is another end, which is the final expansion. And in between are the pulsations, which may last billions of your years. However in terms of infinity, what does it mean?
Perhaps Joshua can explain it thus, it is as looking into the night sky from the surface of the earth. A clear night sky, where the entire sky is filled with little dots of light. Some are brighter and some are less bright. Naturally you know that those are stars, but imagine that behind each of those little points of light are more points of light, and ever more points of light, and if you were to be able to see all of the points of light at once, there would not be a dark sky, it would be brilliant white light. And that could be construed as infinity. It is the light upon the light that can be viewed in the mind as expanding forever in all directions, that is infinity.
(Are there different universes?) There are other universes, there are also multiple universes that extend into multiple directions, not only the directions that you can imagine, directions of which you have no concept. However it is simply better to remain within our own universe, for those others are seemingly so bizarre that, in fact, it would be impossible to comprehend their existence, let alone the way that they operate.