Unable to send mail. How do you set up an outgoing server?

See if this support article can help:

• Add or remove email accounts in Mail on Mac - Apple Support 

Are you talking about installing settings in Mail? If so, the process is to open Mail and create a new account. Then you will be prompted to answer some questions. (Mainly your email address and who the service provider is.) Mail then contacts your email service provider's web site and attempts to connect to it to confirm that the settings, ID and passwords are correct. If not you have to go into Mail's Preferences and manually make any needed corrections. I hope this information is helpful. If not, then please state more specifically what the issues are.