i am going to use a battery with the Capacity: 22.2V, 10000mah 25c or Capacity: 40V, 10000mah 25c i would prefer to use 20v as its smaller and cheaper but would this be enough to power a electric skate board motor?
I use 6S which is 22.2v and it is good for a first build. As long as you get a motor with a kv of 245 (or around that) you will get decent speed (with the correct gearing). A higher voltage will be more efficient and will get better speed and range.
And what dose mah do for instance my batter is 10,000 mah
If you times the voltage by the ah not mah (1000mah = 1ah) you get wh. The more ah and voltage you have, the more wh. 1km = roughly 10wh
Amps are the capacitance of your battery. The amount of energy stored in a pack or cell. Volts are sort of the speed of the energy which effects the RPM of your motor and overall wattage.