Hi Najm,
have you tried the test examples shipped in the tarball (src/pl/plpgsql/test)?
In addition, you can find *lots* of examples (mostly with Hungarian comments)
on ftp://pc10.radnoti-szeged.sulinet.hu/home/kovacsz/Linux/PostgreSQL/strukturak/*
PLPGSQL is one of the best things in PostgreSQL. Easy and useful.
Feel free to ask if something can not be understood.
Zoltan