Positive and negative charge
Like charges repel and unlike charges attract. Electrons carry negative charge and protons positive charge, with balanced contributions making a neutral atom. Macroscopic charging usually transfers only a small fraction of a material’s electrons, so electrically neutral matter still contains very large numbers of charged constituents.
References: [1]
Charging by transfer
Contact and rubbing can redistribute charge between materials according to their electronic properties. Accounting for one object’s gain requires following changes in its surroundings. Such processes separate and transfer existing charge rather than demonstrate creation of net charge from nothing by friction.
Conductors, insulators and polarization
Some charge moves relatively freely through conductors, whereas insulating materials can respond through localized displacement. An external charged object can polarize an initially neutral object and attract it. Attraction therefore does not necessarily prove that the second object originally carried an opposite net charge.
References: [2]
From charge to current
Charge is measured in coulombs, while current describes the rate at which net charge passes a cross-section. This separates accumulation from transport. Relating charge movement to energy additionally requires potential differences and fields; equal amounts of charge can correspond to different transferred energies.