Electricity is basically the flow of electrons. The potential to move or 'pressure' is called the Voltage (v, Volts). The rate at which it flows is called the current, (I, Amps). Each different medium the electrons flow through have different properties that restrict or allow current to flow through. This is known as resistance (R, Ohms). There is a constant relationship between these factors,
Voltage = Resistance * Current (V = R * I)This can be manipulated to Resistance = Voltage / Current or Current = Voltage / Resistance. Generally devices are spoken of as requiring a certain power.
Power (W, Watts) = to Voltage * Current (W = V * I).
Most instruction include a circuit diagram. For help understanding it here is our legend for all of the symbols on those diagrams.
When putting DC power sources together, if they are in parallel it adds the voltages together and if they are in series they add the available currents. Eg two 1.5 volt 500mAh batteries end to end produce 3 volts 500mAh. Connected Side by side they produce 1.5 Volts 1000mAh. Like so....