Does your relative read English?
Even if (s)he doesn't, it would be almost impossible to get lost at Schiphol. There are directional signs at every step of the journey. They can't be missed and there are no "gaps" that leave you wondering which way to go next.
By the way - what do you mean by "central area"?
If you mean the arrivals area, tell them to follow the signs for "Baggage hall" /"Arrivals hall". See the pictograms above.
If you mean on to another gate, follow the signs for the correct gate. The gate for the next flight can be determined at the information monitors ("TV screens" in KLM-speak) that are strategically placed.