Best practices for creating intranet sites for different departments of an organization.
You have multiple options to structure your department site hierarchy.
- Each department gets its own site collection.
- Single site collection. all department sites are subsites, just 1 level below the homepage.
- Single site collection. all departments are organized into a hierarchy of subsites according to function.
Each option has its advantage and disadvantage please check this at How to structure sites in your SharePoint Intranet
See also SharePoint Department Site Example
Note: it's recommended to use Team Site template to can save the site as template and be able to reuse it with other departments. for more details check MISSING SAVE SITE AS TEMPLATE IN SHAREPOINT
Here is the video tutorial which will help you understand how to create different departments subsites under one root site with each subsite having different look & feel. This video will also help you to brush up your knowledge as how to navigate between different subsites, embed you tube link in SharePoint, group the list by a particular column and how to apply themes for different subsites