Clerics may select any two of the domains granted by their deity. Clerics without a deity may select any two domains (choice are subject to GM approval).
Every domain has a number of subdomains associated with it. Each subdomain replaces a granted power and a number of spells in the domain's granted spell list. A cleric who chooses a subdomain must have access to both the domain and its subdomain from her deity. If a cleric selects a subdomain, she cannot select its associated domain as her other domain choice (in effect, the subdomain replaces its associated domain). Subdomains can be selected by druids (except the metal subdomain) and inquisitors (if their deity allows it).
Subdomains are treated as equivalent to their associated domain for any effect or prerequisite based on domains. If a subdomain has two associated domains, the cleric can only select the subdomain for one of her domains. If a subdomain ability calls for a saving throw, the DC of the save is equal to 10 + 1/2 the character's cleric level + her Wisdom modifier.