I have a pen. He has a pen. Total is two pen. This is plus.
I had two pens. A pen was lost. So, I have a pen. Total remaining is one. This is minus.
I have two pens. Three other friends have two pens. 4(persons)⋅2(pens/person)=8pens. This is multiply.
How to understand this?
I have one pen. I become really angry and I break it into x pieces. Each time I get angry I break each of my pieces into x even tinier pieces. I become angry y times. I end up with xy pieces.