Difference between Kun, Ter and more

I was watching a Thai show and multiple times I heard the main character say Ter. Rather than kun. I'm not understanding when to use the word. Aren't they the same? If not when should I use this word when I am speaking with someone. Also are there other words people use other than chun and kun. I want to understand better. If there are other words people use more often please let me know. I want to sound more normal than a robot but I also understand I am still learning. Thank you