Nako 11'800ftis located at the east end of Kinnaur Valley and is the last point of interest before you reach the landslide at Malling Nullah between Kinnaur and Spiti Valley. Catch a bus or 4wd to the landslide from Reckong Peo 4 hours, and tell the driver you're heading to Nako. If he isn't headed there himself then he will advise you on getting there.
Nako lies within the restricted area close to the Tibetan border. An Inner Line Permit is required, which is available in Reckong Peo for Rs 150 or Kaza or Shimla for free, and is good for 14 days. It used to be prohibited to stay overnight anywhere within the restricted zone, but this is no longer the case, provided you have a valid permit. Also note that this Inner Line Permit is required only for Foreign Nationals and local people including non-Himachalisdo not require same.
If you've just crossed the landslide from Spiti Valley, ask around at Malling Nullah for a bus or car that can take you to Nako 45 min, or catch a Reckong Peo-bound bus that can drop you at the turn off to Nako and advise you on a connecting ride.