Hi Luis,
try to get around with acs-templating docs mainly "How the Templating System Works" here https://openacs.org/doc/acs-templating/guide/
about working with master and included templates look for "reusable presentation components" in this page doc.
maybe you could checkout openacs-org code from cvs ( cvs -z3 -d:pserver:mailto:anonymous@cvs.openacs.org/cvsroot co -r openacs-org openacs-4 ) and see how it builds frontpage with edit-this-page applications. Look into tcl/openacsorg-init.tcl , www/templates/ and www/templates/widgets to found some ways to change your website.
