This is going to take some time. For one thing I'm out of town until next week and will only have limited time to work on this. For another I want to move pretty slowly so that it doesn't get confusing. Let me know what you think about that.
Now, I want you to remember some other things too:
1) I am not a cosmololgist or a "real" physicist. I happen to have a degree (only BSc level) in physicts but what I learned then has little to do with this question and I've forgotten what I learned so the degree can be discounted completely. That is, I'm not an expert.
2) This is a really, really difficult conceptual area. What we learned in the 20th century is that the universe is absolutely, definitely NOT how we preceive it. Our perceptions are geared to working in the environment we live in and just accurate enough to allow us to survive. However,the actual underlying facts are NOT like we think they are.
3) At some point both you are I are going to have to take some answers "on faith". We can't do the math which is part of the support for what we understand to be "true" about the universe. I'll try to give you some ideas of which parts I understand to be more solid and which are more speculative.
4) I hope that others can start a thread separate from this one to jump in and try to correct any major errors I make. I'll then attempt to clarify what is meant or where I was wrong.
5) Ask, ask, and ask. Don't let things go by that you don't understand. But remember that you will NOT be comfortable with this even if you do get some tenuous grasp of it. It is weird, strange odd and sounds ridiculous. That is, like it or not, the way things are.
I'll jump back in here in awhile (I hope later today with some beginning). In the meantime if you would post as much detail as you can about what you do understand and what you have heard it might help me to guess what we should talk about.