In Sharepoint, content types are the “BIG” thing.

Here is a small answer to a questions that every new site administrator or new end user will have one day.

When you want to add a page or a document in a library, you are doing: “New” -> and you choose a “type of item”, in Sharepoint the type of item is a “Content type”.

To add a content type in the list, you need to go to the library settings and add it to the list of used content type.

To do it:
You need first to allow content type management for the library.
-Go to the “site actions” -> “View all site content”
-Choose your library where you want to apply the content type
-Go to “Settings” -> “Document library settings” -> “Advanced Settings”
-And click on “Yes” below “Allow management of content types?”, validate by clicking OK

Now we can a content type to be used by the list.
-Go to the “site actions” -> “View all site content”
-Choose your library where you want to apply the content type
-Go to “Settings” -> “Document library settings”
-In the middle of the page you will have a content type list (if no, check below)
-Choose “Add from existing site content types”
-And now you will see a screen with a listing of all content types you can use, choose the one you’re interested in and click “Add” -> ok to validate the change.

Now you will be able to choose the content type you need in the list.