So we want 5/6 of 3/10. The concept might be confusing, so lets try something simple. What is 1/2 of 4? 2 of course. Another way of looking at it is that you multiplied the two numbers. It might be hard to think of 4 one half times, but 1/2 four times is 2. So now we just need to multiply the two fractions.
Multiplying fractions is one of the easier operations to perform on fractions since no conversions or changes are needed. You simply multiply one numerator by the other to get the answers numerator, and then do the same for the denominator. For an example 1/2 times 1/4 would make 1/8, and you can think it through. Like before, if we want one half of 1/4 you can pretty easily understand that 1/8 is half of 1/4, since it takes 2 1/8s to make 1/4. You can reason out similarly with a fourth of 1/2. So now all you have to do is multiply 3/10 and 5/6.