In each of your examples, "though" is used in a different way. To explain each:
This is equivalent to "Thanks anyway!". An exchange where it could be used:
A: Do you need any help carrying those bags?
B: No, I've got it. Thanks, though!
Person B is declining person A's assistance, but thanking them for the offer to help anyway.
Your second example sentence:
It is still pretty weird, though.
In this case, though is used to emphasize what comes before it (despite information that came previous to that). You are basically saying:
It is still pretty weird, regardless of [whatever the other speaker just said to make it sound less weird].
An example exchange:
A: It looked like a ghost came out of the closet in the documentary! That's so weird.
B: They explained that; it was just a trick of the light.
A: Yeah, I know. Still pretty weird, though.
So even though an explanation was offered for the ghost's appearance, person A still thinks it's weird.
As for your final example:
Though Gemini love being adventurous, they also crave stability and security in their hectic lives.
In this case "though" is being used to reconcile two seemingly contradictory statements. Consider the rewrite:
Gemini love being adventurous, but regardless of that fact they also crave stability and security in their hectic lives.
The idea here is that you might consider the two qualities incompatible at first glance, but nevertheless they are both true.