Doublet loupes have two lenses (hence the doublet tag) in order to help eliminate spherical and chromatic aberrations- a departure from the expected or proper course. Chromatic aberration (also known as colour fringing or dispersion) is a common problem while spherical aberrations can affect resolution and clarity. To overcome this use doublet loupes for crisper images with the correct colours.
The 10x means that the loupe will magnify an image 10 times, so something 1mm diameter will look as if it is 10mm diameter. This loupe folds into a plastic housing for protection when not in use.