Saying yes is one of the most frequent phrases I say on a regular basis. There are several ways you can express a "yes" response to your Dominant or others.
When a submissive says "yes" it can be as simple or elaborate as the Dominant wishes. This depends on the formality of the relationship and the situation.
Here are some ideas for how you can answer positively in a D/s context.
For example, if your Dominant asked you, "Are you thirsty?"
"Yes, Sir." "This slave would gratefully accept something to drink Master." "Sir yes, Sir" "Yes please, I am thirsty. May I have something to drink?"
Other ways to say yes could be:
"If you wish it Master" "I am thirsty Sir, thank you for caring for me."
Answering affirmatively may not require speech at all. A nod of the head and a look up at the Dominant may be enough to convey your positive acknowledgment.
Remember that slang is not welcome in a submissives speech set in most cases so words like "yeah," "yup," and "uh-huh" should be avoided and considered inappropriate unless that is the Dominant's preference.