It is difficult because it depends on concepts which are not layman-friendly.
that is that they are things we do not experience in our everyday lives and so seem strange and incomprehensible because of this.
Firstly you have to accept the idea that time is not how we perceive it, linear flowing, dependable - it changes, it can speed up or slow down or stop.
If you travel towards a black hole time starts to slow in the intense gravitational field until eventually it stops.
The big bang is like a black hole in reverse. At "Time-zero" there is no time.
No causality, nothing can cause something else because there is no time.
This is beyond anybody's ability to visualise - even our language is completely riddled with verbs and other words relating to time and cause and effect.
Essentially what I'm saying is the question "where did the first particles come from and how?" is actually a question that doesn't make sense in a scientific context because at that point there is no before there is no how because there is no before.
If you're really interested you could do worse than watch Stephen Hawkings YouTube video
https://www.youtube.com/watch?v=WQhd05ZVYWg
I know it's pretty atheistical but it doesn't do a bad job of explaining the ideas (Even though IMHO he really should at least mention Alan Guth who was, I think the first to come up with the key idea in the video)