Two executable files have been generated during the build: demo and test.
These are command-line interface executables, you must run them from your terminal. To see their usages, just run them with the -h option.
Pass it a dumb C++ source code and it will print out the corresponding syntax tree and semantic graph of the code, in a JSON format.
You can see some examples here.
Regarding the test binary, it will just run the test suite. Unless you want to contribute to Scalpel, you probably won't be interested in using it.
If you want to run the standard library test suite, you must use a non-standard-extension-free implementation, such as the one from Apache. You will also have to add some include paths (-I option).
From time to time, you may run into failures. Take a look at the bug tracker to check whether the problems have already been reported. If not, please fill in a ticket! You may also want to report that on IRC or on the mailing list.