To build JAS3 from source you first need to check the source code out from CVS, using the source code instructions.
Before starting you will need to have Java (J2SE 1.4.0 or later) and ant (1.5.3 or later) installed and in your PATH.
Now to build JAS3 set your current directory to the directory where you checked out the source code and run ant. E.g.:
cd jas3 ant
To build and run JAS3 just type:
ant run