Hi Alojzija,
You can get a pilgrim passport in Le-Puy-en-Velay at the sacristy in the Cathedral. You can see the maps from the Miam Miam Dodo guide here:
http://www.chemindecompostelle.com/Selection/CarteFrance.html If you want to buy this guide, it is also available in the sacristy in the Le Puy Cathedral.
To get to Lourdes you walk on the Le Puy route (GR65) as far as either Lectoure or Nogaro, then deviate.
1) You can leave the GR65 at Lectoure (Map 56 in the Miam Miam Dodo for Le Puy) and walk to Auch (Map 56 in the MMD for Arles), via the GR Coeur de Gascogne, for 37km. You then follow the Arles route (GR 653) to Maubourguet (Plan 62) for 71 km. A little after Maubourguet you take the GR101 south to Lourdes for 46km, passing through Tarbes.
2) You can also leave the GR65 at Nogaro (Plan 65 of MMD of the chemin du Puy) and head south for 39km towards Maubourguet, where you will find the GR 101 for Lourdes.
Descriptions of these routes came in a (free) e-mailed French language newsletter 'Les Zoreilles du Chemin'. They say that the first option lets you walk more on the Chemin paths, but that it's advisable to get hold of MMD for the Arles route for the section between Auch and Maubourguet. The second option lets you quit the GR65 at the last possible moment, but you need to walk more on sealed roads between Nogaro and Maubourguet because this route hasn't been marked.
The second way is a more recently created route. It said there would be maps of this route to download in pdf form (from June).
http://www.chemindecompostelle.com/variantelourdes/index.html
Margaret