Okay, so you made a quickie posable prop or a quick knock-off character, or are trying to conform clothing.... and you REALLY don't want to, but have to deal with --eek!-- Joint Parameters! Say you have no clue WHAT these arcane things are? Well you will in about... two and a half minutes. :)
The twist JP has a unique visual representation, it is a white bar with a red end and a green end.
A typical Twist Bar.
Everything beyond the green end DOES move. Everything beyond the red end does NOT move. In between, is the blend zone.
Tip: Usually the red end should stick a bit into the parent, and the green end should quit near the end of the current limb. Everything along the bar will get torqued, so keep that in mind as well. This bar stops behind the frog's eyes, so the eyes don't start to 'smear' sideways along the head as it twists. Everything beyond the green end twists at the same rate.
The other two Joint Parameters (usually Side-Side and Bend) are represented by an X with red and green arms.
A Bend X that is much huger than one would expect
Everything between the green arms DOES move. Everything between the red arms does NOT move. In between the red and green arms are the blend zones.
Tip: For maximum bend, the red arms should graze the back seam of the limb's parent, and the green arms should graze the far seam of the limb's child (ie: the seam between the child and the grandchild.)
These are spheres of influence.
The Inner (green) and Outer (red) MatSpheres
Everything inside the green sphere DOES move. Everything outside the red sphere does NOT move, unless it is also within the green sphere. In between the spheres is the blend zone.
Tip: These should only be required where a branch limb meets a trunk (arm to shoulder, leg to hip, finger to hand), or other intricate joining. The Bend Xs' lines are really infinite planes, and may 'slice' through the parent (or child) limbs further than one would like. The Sphere zones can limit the 'slice.'
Note: The InnerMatSphere can work happily without regard to the Outer. When setting them up, position the Inner until the limb moves as you want. You can copy and paste it to the Outer sphere, and leave it that way, or scale the Outer sphere up a little. The only time you need worry about the Outer sphere is when you need a smooth blending zone.
Also: The Sphere's are really only relevant to the limb and its parent. Concern yourself with the positioning of the sphere edges that touch/overlap the parent (and make sure the Inner sphere encompasses the end of the limb), but do not worry about how they cut the child.
For more detailed information on the Joint Parameters, try Clint's Tutorials!