PostgreSQL help needed

I appologize for not been able to use Chinese inputs.

I need a little help on how to use PostgreSQL to do Security. As well as how to use the Database system trigger itself to send out alarms.

here is the link to my course website.
http://hebb.cis.uoguelph.ca/~dastacey/CIS3200/S2003/project.html

if any of you can help me pointing out how to setup security in db, such as lock table, lock rows within a table ??

Thanks a lot

Ps. i can read chinese.