surely your text (or google!) gives an explanation of how to work with circuits and resistors. Do you have some particular problem, which the concepts can be used to solve?
The basic principle is that
for resistors in series, the current is the same for all of them.
for resistors in parallel, the voltage drop is the same across all of them.
General explanations offered here will likely be no more detailed or comprehensible than what you've already seen. Post a question about a specific circuit and you will very likely get a usable, specific answer.
Calculating Voltage across a Resistor (Parallel Circuit and series circuit)
3 answers
Steve gave you the recipe.
In series, voltage drops add, currents are the same.
In parallel, currents add, voltage drops are the same.
In series, voltage drops add, currents are the same.
In parallel, currents add, voltage drops are the same.
If I have 2 resistor values 1 being 12 the other 18 how do I calculate the third one