Solar panel specification
Generally speaking, solar panel specs are given for mostly Standard Test Conditions (i.e. under 1kW/m² sunlight intensity, at 25°C ambient temperature, etc).

it's specified that it produces 6V ...

This is probably the open-circuit (i.e. unloaded) voltage generated by the solar panel. This voltage is the maximum voltage that can be measured under STC.

... and 100mAh.

mAh is a unit of charge - \$\mathrm{Q = i \cdot t}\$ thus \$\mathrm{Coulomb = Ampere \cdot hour}\$ and is not a parameter for a solar panel. At least, for ones that I've seen If there's a solar panel with charge specification, please someone let me know. Instead, solar panels have short circuit current specification which indicates the maximum current that can be drawn under STC. So, the product that you are interested in has built-in battery-like storage (I don't think so) or there's a typo (Most likely).

PS: I agree with what @Chris says. Googling &quot;how to read solar panel specs&quot; can bring you lots of info.