Step 1: First we have to navigate to SharePoint online admin site as a tenant.
Step 2: Here in SharePoint admin center select site collections. In site collections we have navigate through New -> Private site collection,
Now we will get a popup window where we can provide all the required information to create our site collection.
Here we can provide the title, web site address, choose template, set time zone, administrator account. After giving all info click ok.
Now we have a new site collection on which we can create our SharePoint app.