This work mainly focused on divertor tokamaks, but most of the arguments and principles can also easily be adapted to other concepts like limiter devices. Results from the 2D SOL transport code B2SOLPS0.5.2D as well as simplified models were used as tools to identify the basic physical mechanisms and apply this knowledge to the design of the Small Size Divertor Tokamaks (SSDT). The effect of the drifts and currents was addressed in this review, including the derivation of the basic equations. This was necessary to get closer insight into the physics of the formation of large radial electric fields close to the separatrix, ion, electron internal transport barrier, as well as in-out asymmetry between the divertor legs and the influence of the toroidal momentum input on this asymmetry.