You will need to, of-course, clone the repository. After you have the repository you will need to download and build Astron's dependencies. See the building readme for instructions.
After setting up your environment you can compile with any of the following:
For release:
cmake -DCMAKE_BUILD_TYPE=Release . && make
For development (with Trace and Debug messages):
cmake -DCMAKE_BUILD_TYPE=Debug . && make
For development (without Trace and Debug messages):
cmake . && make