If a creature wields both natural and manufactured weapons the creature gain all of the attacks it would have if using only manufactured weapons and additional gains one attack with each of it useable natural weapons at a -5. For example a 7 HD monstrous humanoid with 8 cleric levels would have a BAB of +13 thus would have attacks of +13/+8/+3 if only using manufacutred weapons and if only using natural weapons it would have attacks +13(bite)/+8(claw)/+8(claw) (if bite is the primary natural weapon if claws are primary then the attacks would be +13(claw)/+13(claw)/+8(bite) ). If using both natural and manufacutred weapon the cleric would have attacks of +13/+8/+3 and +8(bite)/+8(claw)/+8(claw) if using a weapon that did not require the use of his hands to wield (such as unarmed strike), +13/+8/+3 and +8(bite)/+8(claw) with a one-handed weapon and no shield, +13/+8/+3 and +8(bite) with a two-handed weapon or a one-handed weapon and a shield.
Here are the rules from the SRD
"Manufactured Weapons: Some monsters employ manufactured weapons when they attack. Creatures that use swords, bows, spears, and the like follow the same rules as characters, including those for additional attacks from a high base attack bonus and two-weapon fighting penalties. This category also includes “found items,” such as rocks and logs, that a creature wields in combat- in essence, any weapon that is not intrinsic to the creature.
Some creatures combine attacks with natural and manufactured weapons when they make a full attack. When they do so, the manufactured weapon attack is considered the primary attack unless the creature’s description indicates otherwise and any natural weapons the creature also uses are considered secondary natural attacks. These secondary attacks do not interfere with the primary attack as attacking with an off-hand weapon does, but they take the usual -5 penalty (or -2 with the Multiattack feat) for such attacks, even if the natural weapon used is normally the creature’s primary natural weapon."
