How would you explain mk in text to someone new?

if it comes straight after you asked something, they're just agreeing. the cold one is a lone "k".

It's "mmkay", basically okay. That's all it means. The bit worth explaining to someone new is the tone. "ok" is neutral, "mk" can read as a bit flat or unimpressed depending on who sends it and when. From a friend who always texts like that it means nothing. As a one-word reply to a long message it can come across slightly dismissive. Nothing to turn on, it's just slang.