The first figure is the magnification, the second figure is the diameter of the objective lens in millimeters. The larger the second figure the more light the binoculars collect. A large magnification is less use than light collecting.
For looking at stars / astronomy a 7 x 50 is better than a 10 x 50 as the 7 x 50 gets more light in relation to the magnification so the image is brighter.
Also remember that anything over 7 to 10x magnification is going to need a tripod to be much use, as hand holding always causes a slight shake and the higher the magnification the more the shake is magnified.
All in all a 7 x 50 is about the best for general use.