You need to create a database named xcms (or something else). Use the
xcms.sql file as a template. With mysql:

   mysql <xcms.sql

Then you need to mount the application:

   papp-admin --app xcms \
              --appset default \
              --path xcms/xcms.papp \
              --mount /uri \
              --config 'database => new PApp::SQL::Database "", "DBI:mysql:xcms", "user", "pass"'

It is easiest to do using the admin web interface. After that, xcms should
be visible under the /uri-URI on your server, or using the exec.cgi
script, under /cgi-bin/exec.cgi/xcms.