Content Types are ubiquitous within SharePoint. Content Types are more or less column groupings with certain default settings depending on the type of list or library you create. By default, you’re using Content Types because everything within SharePoint is driven by Content Types.
For example, a Contact Content Type contains fields such as Last Name, First Name, Company, Job Title, Address, Phone, Email Address, Web Page and a number of additional fields.
A Document Library Content Type includes fields such as the document name, a friendly title, the creator, last modified, and includes the link to the document itself.
Content Types creating at top-level sites, like site columns, will be available to that site’s subsites as well. A Content Type can only exist within a Site Collection or at the Tenant level.
Be default, most users won’t even know about Content Types, and this is by design. Out of the box, Lists and Libraries come with the “Allow the Management of Content Types” feature switched to the OFF position.
To turn on this ability, navigate to the list in question, choose the LIST tab, then List Settings, and Advanced Settings. Set the “Allow Management of Content Types” to YES and you will be able to modify or hide fields.
Be judicious with this feature and test it first before you put a lot of data into your lists. Document Libraries for example lose a few features when you turn on the ability to manage content types, however you need this feature turned on when you are working with templates, so it’s something where you need to make a conscious decision as to when you will use the content types on document libraries and when you don’t.
Applying Content Types can save you quite a bit of time, because all the column configurations have already been applied. Also, it’s nice to know that any changes you make to your Content Types within your site lists, they will only affect the current list or library, meaning that the default settings on the Content Types will remain intact for when you want to apply them to another list at a later time.