How to determine table definitions

Hello -
I am brand new to PostgreSQL and am trying to list the field information
for a specific table in a database. I would like to be able to query
the pg_attribute table, but can not determine the necessary "attrelid"
from the fields in the pg_class record for my table of interest.

Alternatively, is there a utility that just displays table-specific
information including fields, field lengths, datatypes, etc.?

Thanks much!
Diane