Electricity is stuff on the move. The stuff is charge, measured in coulombs (C) — one coulomb is about six billion billion electrons, a crowd far too big to count one by one. Current is the traffic report: how much charge walks past per second. Its unit is the ampere (A), and the whole definition fits in one breath — $1\ \mathrm{A} = 1\ \mathrm{C/s}$, one coulomb passing by, every second.

The chapter's first formula ties them together: $Q = I\,t$ — read aloud: Q equals I t. A current $I$ flowing for a time $t$ delivers charge $Q$. (Why Q for charge and I for current? History — physics keeps old nicknames the way families do.) And the units always tell you who is who: amperes flow, coulombs pile up, seconds just tick.