The trailhead is placed at Lescun, a small village in the french Vallée d'Aspe (Departement Pyrenées Atlantiques). You can reach it from Pau and Oloron St.Marie, driving southwards to the spanish border (follow the "Col de Somport" signs) or from the spanish town of Jaca. This latter access will mean driving north to the ski resort of Candanchú and crossing the Col du Somport, a 1600 meters mountain pass with a winding road on the french side. A tunnel is already open to make this crossing easier.
From the village of Lescun follow the dirt road to the mountain hut ("réfuge") of Laberouat. From that point on you will have to follow the red-and-white paint signs of GR-10 westward to the Col des Anies. From this mountain pass take the path south, around the pic d'Anie, to join the western route.
No special needs, except for winter season. In this last case make sure to carry ice axe and crampons, apart from good winter clothing