To send a newsletter you have to have already added one. Select the one you want to send. Then select the "From Address" that the system will use when the emails are sent out. When you select the newsletter the system will auto-populate the subject field. You can change this if you wish.
Then select the people you want to send the newsletter to. To select all, click on the check box at the top in the table header.
Emails are monitored very closely and any abuse (sending spam etc) will not be tolerated. Sending spam emails will cause your account to be suspended without notice.