Take BART one stop to the San Bruno (not the other direction to Millbrae) station. The BART San Bruno stop is co-located with the Tanforan Plaza shopping mall.

Unfortunately, BART will charge you $4.05 each way for this short trip, but it's still the most convenient way to do it without a car.

If you have a car, take 380 to El Camino Real (first exit) and turn right, you'll see the mall.