"Sağ ol" literally means "be/stay alive" but we use it as a "thank you" It's actually an example of imperative form, yet it doesn't have any rude or impolite sense since it's for thanking. Sağ ol. - Imperative, second person singular; therfore no suffix. Sağ olun. - Imperative, second person plural; "-n" As Nazim explained, any kind of second person plural sentences can also be used for being polite.

"Sağ olun" is used in 2 different situations: 1. When you thank 2 or more people - Thank you all, both. 2. A polite form to thank someone (usually, talking to elderly people, strangers or people, you don't know well).