Here are some example situations that require different sets of instructions:
The instruction to allow access to a single user is:
require user {username}where username is an entry in the .htpasswd file.
The instruction to allow access to a group of people is:
require group {groupname}where groupname is the name of a group in the .htgroup file.
The instruction to allow access to any user inside a certain domain is:
order deny,allowwhere domain name is, surprisingly enough, the name of the domain to allow access to (ie. .cec.wustl.edu)
deny from all
allow from {domain name}
The instruction to deny access to any user inside a certain domain is:
order allow,denywhere domain name is, again, the intended domain name to deny access to.
allow from all
deny from {domain name}