Hi Vinod Survase,
Thanks for posting in the Q&A forum. This is a pretty expansive question, and it seems that you are starting the exciting journey of exploring Microsoft Graph.
Microsoft Graph is the gateway to data in Microsoft 365. Providing a unified programmability model that can access data in Microsoft 365, Windows 10, and Enterprise Mobility + Security. (See chart below)
A great way to start learning more about Microsoft Graph is to use our on-line learning paths/module/videos to see examples with code.
Browse learning paths and modules Microsoft Graph
Microsoft Graph Fundamentals for Beginners
Also, we have tutorials showing implementations of Microsoft Graph using Delegated (user) / App-only authentication in .NET, Go, Java, JavaScript, PHP, Power Automate, PowerShell, Python and TypeScript (just to name a few).