Question about saying "Thank You" to strangers in Korean
I understand the different levels of formality in Korean, and how you can say either 감사합니다, 고마워, 고마워요, 감사해요, etc. depending on who you're speaking to.
However, I have a question more-so about a few certain situations.

1. In America, when leaving a store/after purchasing something we typically say "Thank You" as we leave. In Korea, do you say thank you? If not, what do you say?

2. I'm also curious about what to say at restaurants. Do you say "thank you" when they bring out your food or refill your drink? Or not?

I've been very curious for a while so any explanation would help me out a lot. Thanks!

Question

Question about saying "Thank You" to strangers in Korean
I understand the different levels of formality in Korean, and how you can say either 감사합니다, 고마워, 고마워요, 감사해요, etc. depending on who you're speaking to.
However, I have a question more-so about a few certain situations.

1. In America, when leaving a store/after purchasing something we typically say "Thank You" as we leave. In Korea, do you say thank you? If not, what do you say?

2. I'm also curious about what to say at restaurants. Do you say "thank you" when they bring out your food or refill your drink? Or not?

I've been very curious for a while so any explanation would help me out a lot. Thanks!

Answer

1. In America, when leaving a store/after purchasing something we typically say "Thank You" as we leave. In Korea, do you say thank you? If not, what do you say?
yes, we do.when you have bought something in the store, you could say  감사합니다. 안녕히계세요(thank you. good bye(polite expresstion)) to staff leaving there 
2. I'm also curious about what to say at restaurants. Do you say "thank you" when they bring out your food or refill your drink? Or not?
yes, we do. it is polite to say 감사합니다. we do not say  고마워 to elder people or strangers. 고마워 is usually used to friends and people who is younger than me
it is common to say 감사합니다