You can directly use SYS.UTL_SMTP package from your e-mail sending code. But for ease of use i recommend creating the following procedure. Because if you use UTL_SMTP directly from your code, you have to write UTL_SMTP package parameters again and again. With this following procedure you can easily send e-mails from your e-mail sending code.
Please carefully examine and change parts specific to your site on the following code. Like "smtp_hostname","smtp_port".