Like your solar arrays, batteries can be wired in series to increase voltage, or in parallel to increase the storage capacity of the array. For wiring in series, the positive terminal is connected to the negative terminal – much the same way that you put batteries in a flashlight, and for the same reason. When hooking them up in parallel, you hook them up positive to positive and negative to negative.
Most of your home appliances want 12-volt current, and most commercial solar battery systems run with multiple 12-volt cells. Sometimes, for specialized needs, you'll need to run them in series for peak demand at 24 and 48 volt draws; again, knowing what your appliances need (covered earlier) is an important part of the process. Because batteries provide DC current (until you run through an inverter) and are hooked up to transfer DC between them, it's very important that your cells and the wiring that hooks them up be of the appropriate size and capacity; doing otherwise reduces efficiency, and can run the risk of electrical fires.
While we're talking about hooking batteries up to contacts, it's important that all your contacts get tightened evenly, and that the contacts be matched appropriately. You want to avoid differences in resistance in the contacts, as this will reduce charge to one battery string and reduce battery life. Also, put the main positive lead, and main negative lead on opposite corners of the array; this will even out any differentials in charge potential.