By using the OsmoSDR block you can take advantage of a common software api in your application(s) independent of the underlying radio hardware.
For installation and usage guidelines please read the documentation available at http://sdr.osmocom.org/trac/wiki/GrOsmoSDR
For the impatient :) a short excerpt:
The gnuradio source requires a recent gnuradio (>= v3.6.4.1) to be installed.
Before building the source you have to make sure that all the dependencies (see list of supported devices above) you are intend to work with are properly installed. The build system of gr-osmosdr will recognize them and enable specific source/sink components thereafter.
Please note: prior pulling a new version from git and compiling it, please do a "make uninstall" first to properly remove the previous version.