Hi Mario,
I'm not an archaeologist, but I'll do the best I can to answer your question. There have been many theories about the Nazca Lines, but one of the most recent theories is that they are paths meant to be walked by people participating in religious rituals associated with the acquisition of water. Archaeologists have been trying to find a connection between the Nazca Lines and the motions of the Moon, stars and planets for years, but computer models have not been able to find any obvious link to astronomy. However, scientists did find what appeared to be a link between the lines and the Sun's positions on the horizon during the times of the year when water flows down into the Nazca basin from heavy rains in the Andes. We really don't know for certain what the Nazca Lines were used for, but this theory seems plausible.
Kris