The file .pgpass in the home directory is a file that can contain passwords to be used if the connection requires a password. This file should have the format:
hostname:port:database:username:password
Any of these may be a literal name, or *, which matches anything. The first matching entry will be used, so put more-specific entries first. When an entry contains : or \, it must be escaped with \.
The permissions on .pgpass must disallow any access to world or group; achieve this by the command chmod 0600 .pgpass. If the permissions are less strict than this, the file will be ignored.
Read the upstream documentation. For corrections, first check the current manual.