Microsoft has designed a Modern Team site experience to make it easier for anyone to create beautiful, dynamic, and mobile-friendly sites. This article explains, how to convert your classic site collection to a modern experience site.
Today, a modern site can be created under Office 365 Group with template STS#3 or sub site of any classic site but there is no option to create a root site collection with modern experience. But what we can do is, convert our classic site collection to modern experience with merely a few clicks.
Let's create one new site collection with classic experience using Admin center.
Below, the site is created with the classic experience.
On all site collections, there is an option, “Connect to new office365 group” except the root site collection because it’s not advised to change the root site collection as Office365 group.
This option will convert your team site to an office 365 group with the same URL. Click on "Let's get started" button.
Here you need to define a group. Provide group details and click finish.
You will see a brand new user interface.
Conclusion
We just learned how to convert a classic site to a modern site.