1) Build Schema from Database (Make sure config/database.yml is configure with the Database)
php symfony propel:build-schema
2) Build Models
php symfony propel:build –model
3) Build Forms
php symfony propel:build –forms
3) Build Filters
php symfony propel:build –filters
4) Cache Clear
php symfony cache:clear

For complete commands list vist http://symfony.com/legacy/doc/reference/1_4/en/16-Tasks.