Please can someone walk me through step-by-step weight painting and armature. ive tried every tutorial ive downloaded numerous amounts of files to see how they work. but i dont get it!
this is what i dont get.
i can set up the armature fine but i dont know how to be in pose mode and weightpainting mode at the same time?
can someone PLEASE Help.
it would be much appreciated 
I assume you want to select an individual bone in the armature to weight paint ? … If so just select your armature and Ctr-Tab into Pose Mode . Then select the bone you want to weight paint . Then select your mesh and go into Weight Paint Mode . The bone you selected previously should be highlighted . Weight paint your mesh as desired .
You can also select (RMB) other bones within Weight Paint mode now . You don’t have to go back to Pose Mode to select other bones .
Also just to make your life a little easier you can enter the Face Select Mode in Weight Paint by pressing the hot key “F”. This limits the area to be weight painted to the faces selected and makes for more organized weighting of the mesh .
And a final tip; try using the “From Closest Bones” option that becomes available when you parent the armature to the mesh . Do this after you set up your armature’s envelopes (use the Envelope view type for the bones) to roughly cover your mesh . This will automatically set up weights for your bones, and with some practice with setting the envelopes up you will save a lot of time and will only need to weight paint minor tweaks that you couldn’t get to with the envelopes .
i dunno if this helps, but as my esteemed collegue just pointed out, pose mode is for armatures, weight paint is for meshes. There can be only one in edit mode at a time, but there is a weight painting for each bone.
The confusing (or convenient … depending on your point of view) thing is that CTR-TAB is used for both POSE mode (when an armature is selected), and Weight-Paint when a mesh is selected
If you select the armature, switch to Pose Mode, then un-select the armature … with “a” for example, but then don’t select the mesh before pressing CTR-TAB (to go into Weight-Paint), you’ll de-activate Pose Mode for the armature, even though the armature was not “selected”.
In fact the armature WAS selected,; what wasn’t selected was any individual bone. f you then select the mesh, and go to weight paint mode, youll find that the armature is no longer in Pose mode.
So that might be what’s happening …it’s happened to me more than a few times 
To make it easier to tell if you’re still in Pose mode for the armature before you go into weight-paint, make sure that you select a bone (so it turns blue), before you then select the mesh and go to weight paint mode … after going to weight paint mode that bone should still be blue. … and a further check is that after switching to weight-paint mode, your mesh should immediately change to; Blue … red …oange… … i.e a variety of colors indicating you’re in weight paint mode. The “mode” dropdown in the 3d header will also switch to Weight Paint.
Also, after selecting the Armature, going to Pose mode, then selecting the mesh, if at that point you happen to press “a”, to “deselect” your mesh … it will actually still be selected, as you can tell by looking at the bottom left corner of the 3d window. So pressing CTR-TAB at that point WILL set the mesh into Weight paint mode.
Mike