Remember that multiplying is how many times you add a number to itself. If you multiply by 3, you add the first number to itself 3 times.
When you multiply a given number by 1, you get the first number (it doesn't change).
When you multiply by a number less than one, say, one half, you'll end up with half of the original number --> a smaller number.
When you multiply a number by more than one, you will get a number bigger than the original because you are adding it to itself more than once. Even if it is a fraction or decimal, if it is greater than 1, then the new product will be larger than the original number.
Hope this helps! :)