“I assign vertices to a vertex group, and those verteces doesn’t follow the bone at all.”
“Automatic Weighting”, adds it’s own vertex groups, you do not need to add your own, unless you add more bones AFTER you have used automatic weight painting.
You need to confirm that you are selecting the correct bone to be used for painting in POSE mode.
Go into OBJECT mode
Right mouse click the armature, and make sure it is in POSE mode.
Right click the bone you want to assign vertex weights to and then right click the mesh, go to weight painting mode.
Start painting your weights.
If the painting does nor start, you are either using weight strength 0; have accidently activated the weight paint mask, and no faces are selected, or you have accidently lost your “bone lock”.
To quickly find a bone while weight painting: you can press the TAB key, while the mesh is selected and enter EDIT mode. Then you can see the bones.
Place the mouse cursor over the bone you want to select and press TAB again to get back into weight painting mode, (DO NOT MOVE THE MOUSE).
When you now right click you will have selected the bone that is under the mouse through the weight paint mesh, (you can select bones while weight painting, even though they are hidden by the mesh.
Care should be taken while weight painting, that you do not:
accidently right click and choose another bone, WHILE in weight paint mode
do not “over paint” onto an area of the mesh, that you did not intend to paint, (can be a pain to locate the overpaint later on). keep the brush small or zoom in closer to your work)
sometimes “automatic weights”, especially if used in conjuction with, “envelope” weighting, can “bleed” over to an area, not wanted: ie. One leg of a character is automatically weighted, but the inside leg of the opposite leg, also receives some weighting value. This you will need to carefully correct yourself, or reduce the envelope size, if you are using envelopes.
If you set your vertex group names up properly, you can also use mirrored weight painting, that duplicates your weight painting strokes onto the opposite side of your mesh, reducing your work load, (depending on your Blender version).
Hope this information helps Tymechran.