The DMAIC process is the core of Lean Six Sigma methodology. It is an acronym for Define, Measure, Analyze, Improve, and Control. The ultimate goal is to achieve continuous improvement, reduce defects, enhance quality, and optimize processes within an organization.
As stated below are the purpose and actions of each stages for easy understanding:

Define:
Purpose: Understand the problem or opportunity for improvement.
What to do:
• Clearly state the problem and how it affects the organization or customers.
• Decide what’s included and excluded from the project.
• Identify important people and their expectations.

Measure:
Purpose: Measure and learn about the current process.
What to do:
• Collect relevant data and choose the right measurements.
• Create visual diagrams to see how things work currently.
• Figure out how well the process is performing right now.

Analyze:
Purpose: Find out why things are the way they are.
What to do:
• Dig deep to discover the main causes of process problems.
• Study the data to understand how the process behaves.
• Use math and tools to test ideas and find out what matters most.

Improve:
Purpose: Make changes to fix the root causes.
What to do:
• Think up ideas to solve the problems.
• Try out changes on a small scale to see if they work.
• Make adjustments and put changes in place everywhere.

Control:
Purpose: Keep things running smoothly.
What to do:
• Set up rules and checks to maintain the improved process.
• Keep an eye on things to catch problems early.
• Make plans for what to do if things go wrong and write down how things should work.