Tuning sets the tension of the strings so the piano plays at standard A440 and every note is in tune with the others. This is the service most pianos need once a year.
Regulation adjusts the moving parts behind the keys: leveling the keys, setting the hammers and dampers, and aligning the pedals. It restores even, responsive touch across the keyboard. Older and heavily played pianos drift out of regulation as the felt and wood parts settle and wear.
If notes sound wrong, you likely need tuning. If the touch feels uneven, keys are heavy, or notes repeat slowly, you likely need regulation. Clare's can tell you which during a visit, and handle either one in your home.