To get to Gibraltar by bus you need to travel to La Linea bus station. La Linea de la Concepción is the Spanish frontier town on the border with Gibraltar. As you come out of the front entrance the iconic Rock of Gibraltar is clearly visible.
The Spanish border entry point into Gibraltar is very close to the La Linea bus station. Perhaps 5 minutes walk without a suitcase and 8 to 10 minutes if you are trundling a suitcase, but very walkable. Step out of the bus station and there’s a great little cafe next to the roundabout in front of the La Linea de la Concepción bus station. Gibraltar airport is no more than five minutes walk after you cross the border.