Notifications usually occur after the build is done. You can add post build actions, that are, as the name suggests, tasks executed after the build.
You'll find an option, E-mail Notification that allows you to send an e-mail when the build is broken.
All you have to do is fill in the e-mail address.
But what if you want to send e-mails even if the build is not broken? Or if you want to include logs, pictures, or more recipients? There are plug-ins that gives you more options for notifications.
Not only with e-mails, there are plug-ins for sending Skype messages, launching USB missiles, using GTalk, Jabber, IRC, among other notification channels.
Below is an example picture of email-ext plug-in, that lets you to add more options when sending e-mail notifications.