Resistors Series and Parallel
Just a small layman formula note. This is only for how Ohm resistance by itself is added when put in serial or parallel and does not mention how volts or current relates to it. Just google Ohm's law if you're looking for more info, I often use it myself when creating things like LED arrays.
Resistors in series:
10+10+5 = 25 Ω
Resistors in parallel:
E.g. 10+10+5 = 1 / ((1/10)+(1/10)+(1/5)) = 2.5 Ω
Parallel Note: Imagine a narrow water hose with water flowing through it. Now imagine you have 2 of them. Now the water has less resistance, as more water will flow through them combined. So, if you have 2 resistors at 10 Ohm in parallel 1/((1/10)+(1/10)), you have a new resistance at 5 Ohm because of the double flow paths.