Paint the weights. Pose to check.

Each vertex follows the bones in proportion to its weights. Paint them in Weight Paint mode as in Blender, bend the bones and fix what breaks: the elbow, the zero weights, the symmetry and the limits of a game engine.

STAGE

3D Viewport Weight Paint

Zero Weights Wireframe Rest Position

Blend Weight 1.00 Radius 50 px Strength 0.50 Auto Normalize X-Mirror Front-Face Only

MMB orbit · Shift MMB pan · Wheel zoom · Ctrl LMB select bone

LMBPaintCtrlLMBSelect boneFRadiusShiftFStrengthRRotate boneAltRClear poseCtrlZUndo

SAME KEYS AS BLENDER

Shortcuts you can use here

Keys work while the mouse is over the workspace, just like Blender sends keys to the editor under the pointer.

LMB: Paint with the active tool on the active vertex group
CtrlLMB: Select a bone: its vertex group becomes the active group
F · ShiftF: Change the brush Radius / Strength with the mouse; click to confirm, Esc to cancel
R: Rotate (bend) the active bone with the mouse; click to confirm, Esc to cancel
AltR: Clear the rotation of every bone (back to the rest pose)
CtrlP: Parent menu: With Empty Groups, With Automatic Weights
MMB · ShiftMMB · Wheel: Orbit / pan / zoom the view
Numpad 1 3 7 · Home: Front / right / top view · frame all
CtrlZ: Undo · CtrlShiftZ redo

BACK IN BLENDER

A good skin, step by step

This lab shows a simplified Blender: tube-shaped meshes, bones that bend and twist, and the tools that matter most. The weights, the colours and the operators behave like Blender's.

Name the bones with .L and .R and apply the scale of mesh and armature (Ctrl A › All Transforms) before skinning.
Select the mesh, then the armature, and Ctrl P › With Automatic Weights. It is a good start, never the end.
Select the armature, then Shift-click the mesh so it is active, and switch to Weight Paint. Ctrl-click bones to change the active group.
Turn on Auto Normalize in the tool options and Zero Weights › Active in the overlays.
Pose the bones to extreme positions while you paint: problems only show up in a pose. Use Blur for smooth joints.
Paint one side and use X-Mirror or Weights › Mirror. Before export: Limit Total, Clean, Normalize All.