1) extract tigress-3.1-bin.zip in /tmp

2) cd /tmp/tigress

3) export TIGRESS_HOME=/tmp/tigress/3.1

4) export PATH=$PATH:/tmp/tigress/3.1

5) check if it runs on the example already provided:

tigress --Environment=x86_64:Linux:Gcc:4.6 --Transform=Virtualize --Functions=main,fib,fac --out=result.c 3.1/test1.c

the resulting executable file is a.out; the obfuscated source file is result.c