If you mean that you would like to create a shared iCloud account with a shared iCloud email address and you already have an iCloud account of your own, you can do that by creating a new Apple ID (see https://appleid.apple.com/account), then use the ID to set up a secondary iCloud account on your Mac by going to System Preferences>Internet Accounts (or Mail,Contacts,Calendars)>iCloud and signing in with the new ID. You can then turn enable Mail in this account to create the shared email account. Secondary accounts are more limited than primary iCloud accounts, and will only sync Mail, Contacts, Calendars, Reminders and Notes.
Once the account is created, it can be added to iOS devices by signing in with the ID in Settings>Mail,Contacts,Calendars>Add Account>iCloud.
Or, if your only interest is in having a shared email account, you might consider just setting up a free Gmail account to share.