Personal tutorial how to use magos at sertain points

[NourmeusXL]

Hey there,for long time i've tryed to make my own models,yet either i screw em up,or they look worse than abomonitions do..
So im getting tierd of fails all over and over again,i really wish i knew how to do the following things:
How can i(exsample):use priests head and put on arthas's one and make em fit perfectly,no gliches.
How can i add texture(exsaple again) from abomonition to peasant,with the texture of the peasant changed and model untouched(head,feet,chest,etc.)
How can i add attachments to sertain places of the model(head,hand,back)

Please help me,giving rep.