It's easy. Klick "Draw skeleton" and you can click Joint and then you see which part of body you are using. For example if you use L Hand you are moving your character's left hand.
Let me give you some examples, you know start pose of for example mage:
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Let's make sth with that arms because she is looking like a robot, left:
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right:
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Ok, but that arm is shouldn't be rigid, lets make something with forearm:
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Hm, ok, now she looks like a human, lets do something with second hand, because we wanna make a nice pose, we can make many things with left forearm:
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Hmm, but it's not perfect as well, lets try to fix it a bit, we can use upper arm to help yourself:
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Now we can come back to our forearm and change it again:
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It's still too far away from a boob... sooo, come back to upperarm again:
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Now forearm:
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So, it's better. Now we need to make something with that hand which is in not normal pose...
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Ok, hand is in right place. Now the thing i hate so much - fingers. You need to try every, to see which is for what, so just click on it and change pose a bit, if u r sure its not good finger go to the next. So, I've just found which finger i need to move:
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We can change a few bones in that fingers, they are under our finger joint which we've choosen:
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Now just one thinger bad, find a good joint and change it, to do it I used just 3 joints which I selected:
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So, we have an easy pose, she is keeping her boob, thats nice. Lets wear something on her, she can't be naked:
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How... awful!! Ok, lets keep it. So, thats was how to make a tasty spaghetti bolognese, maybe later I will show you how to use model viewer
I hope it will help you, it's really nice tool, you just need to try every bone. Don't forget about a Draw skeleton, it shows which bone are u moving. Sadly it doesn't work for me - idk why - that sux.