Here are basic schematics with examples of series and parallel connections for batteries.
A combination of Series and Parallel connections increase the battery bank voltage AND increase the amp hour capacity.
Notice that the cables that connect the battery bank to DC load center conductors are pulled from opposite diagonal ends of the bank. Also, generally you would use water miser flip caps on ALL the batteries or none of them. We just wanted to show an example of what they look like in the picture. :)