Serial means one effect's output feeds the next effect. Parallel splits the input into several paths, then sends them to outputs or a merge. Two paths are not automatically stereo: two mono paths carrying the same information can still sound mono. Separate A/B and Stereo mix map outputs differently.
Combining identical, in-phase signals at equal levels can double amplitude, or add about 6 dB. Differences in phase, delay, or filtering can cause reinforcement or cancellation. Keep headroom and check mono. When converting parallel routing to serial, check the resulting effect order and each stage's level. See the routing guide for use in Rigs.
There is no mandatory order. An electric starting point is: gate if needed → compressor → boost/drive → amp → cabinet → EQ if needed → modulation → delay → reverb. Wah and Volume can move according to the goal. Bass can retain a clean low branch while processing an upper branch; some Rigs Bass amp models provide an internal crossover/blend, but other pedals do not automatically protect the low end.
Gain staging monitors level at every stage, rather than only at the final output. A safe final output does not prove every earlier stage is clean. Distinguish intentional distortion from overload. In analysis mode, compare each pedal's IN/OUT; Peak/RMS values alone cannot give a distortion percentage. THD/THD+N requires a defined test signal and conditions. A real guitar already contains harmonics.