What is CDN and why it's important ? What are the most famous CDN s ?

Basm allah alrahman alrahim

Like you said Nasir Mahmood

with modification :

Microsoft CDN

Google CDN

Bigger company servers stronger than smaller servers

CDN is data stored on cloud and it can access faster,  know CDNs are

Amazon AWS

GoogleCloud

Microsoft Azure

CDN is short for content delivery network, it is used to deliver Web content i.e js, css files and other web contents. CDN play a vital rule to speed up web browser page rendering for example if a user visit ten sites and all sites pointing jquery js file to same CDN then no need to download jquery file every time. Moreover CDN provide contents based on the geographic locations so access time decrees.

Some free CDN are

BootstrapCDN

Coral Content Distribution Network

CloudFlare