I have visited Thailand this vacation.
This is a correct and natural way to use the present perfect, assuming the vacation is still ongoing. If not, it would be more natural to use I visited Thailand.
Also be careful with using this to describe a past event. Normally one would say "I visited Thailand that vacation" if the vacation were not ongoing. You could use this here if you were talking about several vacations in one conversation, to indicate you are talking about the vacation currently being discussed.
How did you get there?
I took a flight. It took about 14 hours.
These are correct as well. Here the present perfect could actually change the meaning somewhat. "How have you gotten there?" implies you have gone more than once, and asks what your usual means of travel was. "It has taken about 14 hours" would imply the flight is ongoing.
Adding your additional example from your comments:
A: Where have you been for your last vacation?
B: I've been to Los Angeles.
A: What have you done there?
B: I've visited Universal Studios
These are all correct constructions of the present perfect, but all four sentences should replace the present perfect with the simple past: "Where did you go for your last vacation?" etc.
I think your intuition is generally good regarding the present perfect. In general if an event occurred in the past and you want to talk about it specifically, you should use the simple past, not the present perfect. Use the present perfect to talk about past events that continue in the present, or to talk about past events in a more general way.
All tenses of a verb can be grammatically correct in a simple sentence; the question is whether it makes sense in context. I think what JMB says in the comment is true: your textbook is probably just trying to drill you on present perfect without taking care to provide more contextually accurate examples
