Relevant to Blender v2.31
If we were going for a still picture, our work up to this point would be enough, but we want Gus to move! The next step is to give him a skeleton, or Armature, which will move him. This is called the fine art of rigging. Gus will have a very simple rigging: four limbs (two arms and two legs) and a few joints (no elbows, only knees), but no feet or hands. To add the rigging:
1. Set the cursor where the shoulder will be, press SPACE>>Add>>Armature. A rhomboidal object will appear, a bone of the armature system, stretching from cursor to mouse pointer. Place the other end of the armature in Gus's hand (Figure 4.49, “Adding the first bone, an elbowless arm.”) with LMB. This will fix the bone and create a new one from the end point of the previous one, producing a bone chain. We don't need any other bones right now, so press ESC to exit.
2. Stay in EditMode, then move the cursor to where the hip joint will be and add a new bone (SPACE>>Add>>Bones) down to the knee. Press LMB and a new bone should automatically appear there. Stretch this bone down to the foot (Figure 4.50, “Adding the second and third bones, a leg bone chain.”).
The bones we are adding will deform Gus's body mesh. To produce a neat result, try to place the bone joints as shown in the illustrations.
3. Now place the cursor in the center and select all bones with AKEY. Duplicate them with SHIFT-D and exit grab mode with ESC then flip them with MKEY relatively to the cursor and Global X axis as you did with meshes (Figure 4.51, “The complete armature after duplicating and flipping.”).
Once you've selected all of the bones (AKEY),
the Edit Buttons window should show an
Armature Bones Panel
which contains the Armature buttons (Figure 4.52, “The Edit Buttons window for an armature.”).
Draw Names button
to see the names of the bones, then
SHIFT-LMB on the names in the Edit Button
window (Figure 4.52, “The Edit Buttons window for an armature.”) to
change them to something appropriate
like Arm.R, Arm.L, UpLeg.R, LoLeg.R, UpLeg.L and LoLeg.L. Exit
EditMode with (TAB).
It is very important to name your bones with a trailing '.L' or '.R' to distinguish between left and right ones, so that the Action editor will be able to automatically flip your poses.