One site, two domains
If you'd like both sites to use the same code/modules and database (thus sharing users and some content), use the domain access module at https://www.drupal.org/project/domain

If you'd like both sites to have the same code/modules but not the database, check out Multisite at 
https://www.drupal.org/docs/7/multisite/multi-site-sharing-the-same-code-base