There are many different ways to learn how to multiply numbers. To start off a basic way to learn and feel comfortable with multiplying is by using the times tables. Now the times tables can go up to however high you want but most people go to either 10 or 12 in order to have a better understanding of what is being taught. The link that I will post below will help you understand how to use it step by step.
This is a short video on explaining the basic mathematics on multiplying fractions.