Cap's pass AC & block DC.
Low freq's need bigger caps, & higher freq's need smaller ones.
if the cap had bulged, the plastic label split or pulled down, top rounded, blacked, burned etc, then it needs changing
If your trying to learn current flow, then use a passive circuit, maybe a few transistor/diodes etc, but avoid IC's etc. We just treat them as black boxes & accept that they work, & if they don't, we change them
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