Packages extend the functionality of the Wolfram Language. In order to be able to load its functions into a Wolfram Language kernel with a simple Needs evaluation, a package first has to be installed into the Wolfram System layout.

Note that several Standard Extra Packages are included in your Wolfram System and do not require any separate installation.

You can install your own or any third-party packages with a few easy-to-follow steps.

1. Navigate to File and choose “Install…”.
2. A window prompts you for more information:
   
3. From the “Type of Item to install” drop-down menu, select “Package”.
   
4. From the “Source” drop-down menu, choose “From File …”. A window appears, allowing you to select the package that you want to install. After selecting the package, click the Open button.
   
5. Choose a name for your package in the “Install Name” field and click the OK button.

The installer creates a copy of the package in either your Base Directory or User Base Directory. You can now load the package in your current or any future session by executing the Needs command:

Needs["PackageName`"]

Note that the last character is a tick mark (`), not an apostrophe (’). It is available on most keyboards underneath the tilde (~). Additionally, PackageName should be the same name as the Install Name field during the installation.

Also note that both third-party packages and built-in packages are loaded with this same syntax.