Any other circuit is a combination of series and parallel connections.    If you need to determine values for any part of these circuits you can break them down into their simpler component combinations.  The two more common combinations are shown below.

The hard part is keeping in mind which parts are in series and which are in parallel.
Series connections have the same current and parallel connections have the same voltage.

When solving these circuits the use of the box becomes more complicated, but it can still be used.  Now, some of the cells will have the same values and others will add together.  By writing the complex equation for the circuit variables you can keep them straight.

An example is given below, but don’t repeat these same formulas for other complex circuits since their rules will probably be different.  The concept of the solution will be the same, though.