The site is the core thing to SharePoint and represents the starting point for developers, and without site collection, you cannot start SharePoint development. A Microsoft SharePoint online site collection is a top-level site that contains subsites.
A number of site templates are available which you can use. The subsites share administration settings, navigation, and permissions each of which can be changed for individual subsites as needed.
Create Site Collection
When learning an application such as SharePoint, it is a good idea to create an area where you can perform exercises without affecting the existing environments or users.
Step 1 − To create a new site collection let us go to the site https://portal.office.com/
Step 2 − Select Admin icon and you will see the following page −
Step 3 − Select Resources → Sites, in the left pane. In the right pane, click Add a site.
Step 4 − Following page will open. Enter the required information and click OK.
You can see that the site collection is added in your admin center URL list. The URL is the site collection location at which the administrator can start to create and manage sites.
Step 5 − Click the link and you will see the detailed information regarding that site collection.