hector_localization and sensor fusion of IMU and Odometry

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Hi all, I would like to test hector_localization package. I would like to ask some basic questions about it. (1) If I input IMU sensor data and odometry data to hector_localization, will hector_localization fuse these two sensor data? Can anyone explain about the relationship between input sensor data and output pose estimation ? (2) If I input IMU sensor data only, what should be the output from hector_localization?Can anyone explain about the relationship between input IMU sensor data and output pose estimation? (3)If I input odometry data only, what should be the output from hector_localization? Can anyone explain about the relationship between input odometry data and output pose estimation?

Thanks in advance for your kind support!