Web interface is accessible at http://your.server.ip:8080/openacs/index.jsf.
You should configure your CPE with the URL of ACS, it is http://your.server.ip:8080/openacs/acs. Also you should configure your CPE to send periodic Inform requests to server.
Server responds to Inform RPC and puts information about device into database (configurable via context parameter org.openacs.AutoCreateCPE), compares software version reported and updates software if needed, then compares version of config reported and does the same. After that scripts are run.
Configuration can be done either by using vendor specific configs or configuration scripts. Configs are put to cpe using Download RPC call. It is required that configuration contains it's version number in such a way that it is reported by CPE in Inform call (this is dependant on CPE model). Some CPE's require that the config file had specific name (e.g. user.ini).
Software: firmware images are kept by default in c:\firmware (windows) or /firmware (Linux/Unix) directory (that can be changed in deployment descriptor in context parameter org.openacs.fwbase) which must be writable by user jboss runs under.