Gliese 832B is a gas giant that is 0.64 the mass of Jupiter, and it orbits its star at 3.5 AU. The other planet, Gliese 832C, is a rocky world about 5 times as massive as Earth, and it orbits the star at a very close 0.16 AU. Both cannot harbor life as we know it, as 832B is a gas giant and 832C is too close to the star.
BASED ON A HUNCH
The already discovered planets were seen because of the radial velocity technique, which measures the gravitational effect of the planets on the star. The astronomers had a hunch that another planet may exist between the vast distance of 832B and 832C. They reexamined the data, and concluded that another planet may exist between them.
The newly discovered planet is still hypothetical at this point, and the researchers put its mass at between 1 and 15 Earth masses (yeah kind of a big margin there), and its orbit is between 0.25 to 2.0 AU from Gliese 382 (1 AU is roughly the distance from Earth to the Sun).
Conclusions such as these are not made definitively, but only so that planet hunters and telescopes such as Kepler know specifically where to look.