@Sanmario , I think that @leibode84 has done what you've asked.This works for me:
"it is the point in time and/or in distance at which point a thing starts to exist, prior to which it was not existing."
So, can you now prove that God is the creator of everything with a beginning?
(Again, not that God exists assuming that God is the creator of everything with a beginning)
However, begging forgiveness of leibode84, I think a better question for you to answer right now might be this:
Now that you know what "beginning" is, and can infer what "not beginning" is from that definition, how is it you can assert that there are "things with a beginning" without also inferring that must likewise be "things without a beginning?"
And how would you differentiate between them? How would you recognize which was which?