The shapeshifter is able to change it's shape and take on the skills and spells of that shape. If a shapeshifter changes shape to an animal, then the character will most likely not be able to use a weapon. Changing shape to a sentient shape that can wield a weapon will allow a shapeshifter to use a weapon.

Shapeshifters have the ability to use the following weapon types:

Mace/club at Level 0.
Sword at Level 15.
Flail at Level 35.