Hi,
Advice from above on fingertip conditioning etc not withstanding, I think you should go and have a lesson with a teacher... They should be able to help you with general posture.
Pain in the wrist is always something to worry about and if you're just beginning you don't want to learn how to contort yourself in to a position that works, it should be comfortable if a little alien at first.
The short answer is to have the guitar resting on your left leg if you're right handed, and hold it at such an angle that the headstock is more or less at eye-level - the higher you have it the more natural your arm should feel in playing position. It might even be worth using a strap even when sat down so you can get the guitar at a better angle.
I'm suggesting a teacher because someone being able to see you will probably be able to come up with a more precise diagnosis. Finger tip pain is to be expected, as is some discomfort in the fingers after prolonged playing as you build strength, but pain in the wrists worries me...
I have big shovel hands so can identify with the initial problem, it's also worth looking at different ways to play chords that may give your fingers more space.
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