What is the difference between "know" and "do know"

Could Can someone explain the difference between two phrases below?
- I know something.
- I do know something.

The "do" here is for emphasis depending on the context.  "I do want to know", means that you MUST know or NEED TO know.  "I do know my English" means I REALLY know my English. "Do carry on with your work.", means MUST, under no circumstance should you stop.