Hello Pavithra,
You can find the explanations here:
- OSI model
- For a detailed walkthrough of how packet goes from one device to another. Take a look at this post: End-to-End Packet Delivery Explanation
- If you request hostnames like facebook.com or youtube.com then we use DNS which is explained here.
- Ping and traceroute are explained in the ICMP lesson.
If you still have questions after going through these lessons, let us know ok?
Rene