If you have not made any custom changes during the installation, your Joomla will be set up by default to use the PHP Main function to send email messages. The settings can be modified via the Joomla admin area -> Site -> Global Configuration -> Server. The corresponding settings are found under the "Mail Settings" section.
Keep in mind that the email address which you are using for "Mail from" should be of type email@example.com.
The second option is to use the SMTP Server for sending email messages via Joomla. In this case you need to turn on SMTP Authentication and supply correct details for the SMTP Server you will be using as shown below:
SMTP Authentication - Yes
SMTP Security - None
SMTP Port - 25
SMTP Username - firstname.lastname@example.org (note that you should use the full email address as username including the @domain part).
SMTP Password - The correct password for the email account you supplied as Username.
SMTP Host - This can be your domain name.