Here's a breakdown:
* Да (da) means "yes"
* Я (ya) means "I"
You can use this phrase in various contexts, like:
* Да, я согласен. (da, ya soglasen.) - Yes, I agree.
* Да, я готов. (da, ya gotov.) - Yes, I'm ready.
* Да, я понимаю. (da, ya ponimayu.) - Yes, I understand.