Imagine you have a bunch of toys you want to play with, but you can only play with one at a time. That's like what it's like for a computer with just one "core" - it can only work on one thing at a time.
But what if you had some friends over to play with you? Now you can all play with toys at the same time and get more done! That's kind of like what having multiple "cores" in a computer is like - it can work on multiple things at the same time.
A "micro-thread" is like a little helper that each core can use to work on even more things all at once. So it's like having lots of toys and lots of friends to play with them - you can get even more stuff done in less time!