How can I, in Drupal, install a project that have 2 different websites(frontend) but share the same backend? Is it possible?
Simple answer is YES. What you are trying to do can be achieved by using one of these modules:
The Multi Site installation module (It requires separate database for each site or common database with table prefix.)
The Domain Access module
These are just general suggestions, as there are several ways to achieve your goal. You have to choose the right method suited for your needs. This is a screen-cast which would be helpful for you.
You should probably look at the Domain Access module.
The Domain Access project is a suite of modules that provide tools for running a group of affiliated sites from one Drupal installation and a single shared database. The module allows you to share users, content, and configurations across a group of sites.
The module uses Drupal's Node Access system to determine what content is available on each site in the network. Unlike other multi-domain modules for Drupal, the Domain Access module determines user access based on the active domain that the user is viewing, rather than which group or site the user belongs to. For more information about Node Access in Drupal, see http://api.drupal.org/api/group/node_access/7.