Select the mesh object
Select the armature
Press Ctrl+P
Choose With Automatic Weights
Enter Weight Paint mode
Select the mesh
Select a bone in Pose Mode
Paint weights on the mesh
Use Add, Subtract, Blur, or Mix brushes
Enable Auto Normalize in the Weight Paint options
Use Vertex Groups in Object Data Properties
Create or edit a vertex group for each bone
Assign selected vertices to the active vertex group
Set the weight value before assigning
Use Normalize All in the Vertex Groups menu
Use Limit Total to cap influences per vertex
Use Clean to remove very small weights
Use Mirror Vertex Groups for symmetrical rigs
Use Transfer Weights to copy weights from another mesh
Use Data Transfer modifier for weight copying
Test deformation in Pose Mode
Adjust weights until the mesh bends correctly