To get started with multiples, the easiest way is just to add a number to itself over and over again. For instance, if you want to find the multiples of 3390 using this method, you could start at 3390, and keep adding 3390 over and over: 3390, 6780, 10170, 13560, and so on. Each of these numbers is a multiple of 3390. Usually, this method works with numbers that are easily added to itself. As you get into larger numbers, it can become difficult to continue adding.
Another way to do this, as discussed above, is to use choose any number and multiply it by 3390. To find the first few multiples of 3390, you could just multiply the 3390 by 1, then 2, then 3, and so on, until you have as many multiples as you would like.
There are an endless number of multiples! You can keep using either of these methods to find as many multiples as you would like.