How to Add and Set a Package in WHM?

You will need to create a package before have an cPanel account in WHM.
How to create cpanel Account? Once logged into WHM, go to Add a Package under Packages.
Give a name to the package in the blank for New Package Name.

Note: Package names preceded by a reseller's username followed by an underscore can only be seen by the corresponding reseller. Packages are limitations on resources an account is allowed to use. For example, you may specify how much disk space an account is allotted. These limitations are bundled and saved so that they can be applied to accounts later. This streamlines setting up new accounts, since you can sell predefined packages to your cPanel account holders or resellers.

What is Resources
Quota (MB): Defines the amount of space on the server’s hard drive the new account will be allowed to use. This option is defined in Megabytes (MB). Make sure to consider what kind of content your user intends to host, as this will greatly affect how much disk space he will need.
Bandwidth (MB): Defines the amount of information the new account will be allowed to transfer each month. This option is defined in Megabytes (MB). Make sure to consider what kind of content your user intends to host, as this will greatly affect how much bandwidth he will need.
Max FTP Accounts: Defines the maximum number of FTP accounts that the new account will be allowed to have at 1 time.
Max Email Accounts: Defines the maximum number of email accounts that the new account will be allowed to have at 1 time.
Max Email Lists: Defines the maximum number of mailing lists that the new account will be able to have at 1 time. Mailing lists are handled by an application known as Mailman.
Max Databases: Defines the maximum number of both MySQL and PostgreSQL databases the new account may have.
Max Subdomains: Defines the maximum number of subdomains for the new account.
Max Parked Domains: Defines the maximum number of parked domains for the new account.
Max Addon Domains: Defines the maximum number of addon domains for the account.
Maximum Hourly Email by Domain Relayed: New option in WHM 11.3x version to set email sending per hours.
Maximum percentage of failed or deferred messages a domain may send per hour: This configuration option allows you to define how overages are handled when a domain exceeds the maximum number of emails allowed per hour. By default, additional messages are queued for delivery and sent in the next hour.

Settings
Dedicated IP: Only check this if you want accounts being set up with this package to automatically have a Dedicated IP assigned to cPanel Account.
Select Options: You can check or uncheck the options for Shell Access, FrontPage Extensions and CGI Access, depending on what you want the accounts to have access to.
cPanel Theme: The default cPanel theme that is set for this account when created with this package.
Feature List: If you ever set up a custom Feature List, you select it here.
Locale: The language that the cPanel will be using.

When done, click on Add.