Holy Jesus Christ, thanks for the lecture from someone with more than 7000 posts yet still has no clue he is not the smartest person on earth, bike-wise or otherwise.
I knew how to adjust a derailleur before any of those posts!
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One thing that no one appeared to mention.
The LBS you buy a bike from will usually do "small" adjustments for you usually free of charge.
Even if you manage to adjust it so things seem to work, it might still be useful to have your LBS check it.