At its core fundamental multiplication is just addition that just goes on and on. We often grow up memorizing times tables, but as we progress they are no longer necessary. The only freaky rule of multiplication is the zero property if multiply anything by zero, it becomes zero. The inverse of multiplication is of course division they actually cancel each others operation and are often used in algebra just for that reason.
You will see that the worksheets below progressively get a little more advanced. This differs a lot from our normal alphabetic order for worksheet, but we thought this necessary so people follow the intented progression with the skills.