Learn Turkish: Sağ ol, çok yardım ettin.

Both mean "thank you," but sağ ol is usually more casual and conversational, similar to "thanks" in English. Literally, sağ means "alive" or "healthy" and ol means "be" (the command form of olmak), so you are literally wishing someone to "be alive" or "stay healthy!"

I often see this written as a single word ("sağol"). Which is correct?

The officially correct spelling is two separate words: sağ ol. However, it is extremely common for native Turkish speakers to write it as a single word (sağol) in text messages, on social media, and in everyday casual writing.

Why do we use two words (yardım ettin) for "helped" instead of just a single verb?

In Turkish, there isn't a standalone verb for "to help." Instead, Turkish frequently builds compound verbs by combining a noun with a helper verb like etmek (to do / to make). Here, yardım is the noun "help," so yardım etmek literally translates as "to do help."

How do the suffixes on "ettin" work?

It breaks down into three parts: the root verb et (do/make) + the past tense suffix -ti + the informal "you" ending -n. Notice that the past tense suffix is normally -di, but it changes to -ti here because the root ends in a hard consonant (t). This is a common pronunciation rule called consonant harmony.