There are types of resistance circuits, including Series, Parallel, and Series-Parallel.
Series circuit is at bottom-left and resistances can be adding together to get final resistance total.
Parallel circuit is at top-left and resistances must be calculating by set each resistance in inverse, then add and inverse again in order such as (R1^-1+R2^-1+...+Rn^-1)^-1, you get final resistance total.
Series-Parallel circuit is at right. It look complex, but it's not hard. First, focus on each PoR, parallel of resistance, to calculate, I explained above, and when PoR is done and you can calculate it by adding together.
