Instructions can be found here : http://forge.jboss.org/docs/using/
To go faster and avoid typing too much commands you can use a forge script, copy/paste the following in a text file and save it as scaffold.fsh (or whatever name you want)
new-project --named scaffoldtester;
persistence setup --provider HIBERNATE --container JBOSS_AS7;
validation setup --provider JAVA_EE;