The first number is the magnification,the second number is the diameter of the lens furthest away from you.
The higher the magnification,the darker the image you see will be.It will be very difficult to keep the image 'stable' due to hand shake.
The best magnifications are 6x,7x or 8x.
An objective lens (the furthest away lens) of 30 is suffice.
You will appreciate and see more through a smaller, bright magnification.
For a' that, an a' that,
It's comin' yet for a that,
That man tae man the world o'er
Shall brithers be for a' that. R.B. 1759-96