You can animate biped's body parts as you do other 3ds Max objects: by setting keys for postures at keyframes.
character studio provides three different ways to set keys at the current frame:
Pose the biped body part, and then click one of the set key buttons in the Key Info rollout.
Turn on the Auto Key button, and then pose the biped part. You can transform the parts using transform tools, or you can
copy and paste poses and postures to keyframe the biped.
If you are animating a walk cycle or an intricate hand animation, then you should make use of the three different types of
set key buttons in the Key Info rollout. Each set key button applies different IK constraints, depending on whether a foot
or finger is in a planted state, a move state, or a sliding state. For more information on the three set key buttons, see
Key Info Rollout.
You can also set keys to make hands and feet follow a stationary or animated object. See Animating IK Attachments.
If a Bones system using the IK controller or a particle emitter is linked to the biped, the Auto Key button must be on in
order to position the biped's limbs. This is also true for biped objects if you turn on 3ds Max Trajectories at the top of the Motion panel, or if you choose Views 
Show Ghosting.
The Set Key options on the Key Info rollout have the advantage that you can easily experiment with different poses for your
character without unintentionally setting keys as a side-effect. Use the Set Key buttons to commit the changes you make to
the pose. The Auto Key mode approach is especially useful when you make adjustments to keyframes that have already been set,
or if you are used to working with Auto Key in3ds Max and tend to forget to click the Set Key buttons.
Keyboard shortcut: Pressing 0 (zero) is equivalent to clicking Set Key on the Key Info rollout.
To use character studio-specific shortcuts, make sure that the Keyboard Shortcut Override Toggle is active.
Ground Plane Collision Detection for the Pelvis and Feet
When one or two feet are planted, and the pelvis or a planted foot is rotated, character studio detects collisions of the foot and its toes with the ground plane defined by the planted foot's footstep or pivot point. As the pelvis or foot is rotated, character studio uses inverse kinematics to alter the rotations of the leg joints so that the foot and its toes do not go below the plane defined by the footstep or pivot point.