The specifications of the binoculars are a way to understand how much you can see with the binoculars. It light and how much magnification you get.
- 8 x means 8 x magnification
- 10x means 10x magnification
The number 30 refers to the millimeter lens in aperture. The size determines the amount of light that enters the lens of the binoculars. A larger lense makes you see better in poor lighting.
What are you going to use binoculars for?
8 x magnification is more than enough for the "average user". Larger magnifications requires a bit of training and steady hands.
10x magnification and larger optics are for experienced telescope users, or for use in a controlled environment where you are more stationary.