Every taxiway is marked with a sign, usually a letter, sometimes a letter with a number, like A2. If you contact Ground and they say taxi to active on taxiways A, F, and G, just look for the signs. You should already know which runway is the active, having written down the latest ATIS, by the way. It really helps to have an Airport Diagram, with such info marked on it also. And be ready to copy Ground's instructions on a notepad, they really dislike repeating themselves.
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