A site collection is made up of one top-level site and all sites below it. it is the top level of organization in a SharePoint 2013 web application. The number of site collections you can have in a single web application depends on the capacity of your server infrastructure.A site collection is used to provide a grouping of ‘SharePoint Sites’.Each web application will typically have at least one site collection.
Then enter Title ,description and select Template and click ok button
Here it will take few seconds like bellow window
Once completed a message pop-up will come . Click on the url link to navigate to the newly created site collection
The new Site Collection named Splessons with Team Site template has been created.