Multiplying by 1

Any number multipled by 1 will equal to itself.

For example, $999*1=999$. Same number as the start.

Multiplying by 0

Any number multipled by $0$ will equal $0$.

For example, $999*0=0$. We always get $0$ no matter what we multiply $0$ by.

Any number that has $0$ added to it, will equal to itself.
For example, $999+0=999$. Same number as the start.