To hook your batteries into a circuit treat coupled batteries as a single battery. The lead from the negative terminal (in white above)
is the negative of your new battery. The lead from the positive terminal (in red) is the new battery's positive end.
Why put batteries in parallel?
A reasonable question is to ask why one wants to put batteries in parallel in the first place. After all, it is a bit of trouble.
For a circuit to work Current must be able to flow through it. The voltage determines whether the electrons have enough energy to get moving - that is, for
a current to flow.
You must have enough current to make your circuit work properly. For example, a lightbulb may appear very dim if there is not enough current flowing.
By hooking two batteries in parallel, you increase the amount of time the bulb stays lit. If your batteries are identical, you effectively double that
amount of time - while the Voltage difference remains the same.