Remember that there is a copy of your media in the Camera Roll at the highest possible resolution (which can be transcoded for export) should you need it later.
On the left you see the preview monitor. If you have an external monitor attached, the image will appear on that monitor and not here (there is a red notification message that will show up instead).
If you are showing a video, the Play / Pause / Stop buttons will be active.
The media file size (and export preset for video) will be shown either above or below the preview monitor display in yellow.
On the right are buttons to allow you to distribute this media to various destinations.
FTP will add this media to the FTP queue so that it can be uploaded to your server the next time any FTP transfers are initiated. You can see your media in the list on the FTP queue page, and delete it from the list, if you change your mind later.
Email will send the file as an email attachment at the resolution and file size shown. Beware that files over 10000 kilobytes are generally problematic for email servers. Once you tap the Email button you will have the option to set the destination addresses, subject, and add a textual message.
The Facebook and Twitter buttons, if enabled (you need to setup the Twitter and Facebook apps separately on your device and allow iENG to use their login credentials). Hitting either button will bring up a page where you can modify the default short message text that accompanies your post.
If you are uploading a still image to either Facebook or Twitter, your still image can be resized automatically per your selection on the 'Setup' page.
If you are uploading a video, the YouTube button will be available to allow for an email upload to your YouTube account at the same export resolution that an FTP upload would use (and displayed in yellow either above or below the preview display).
On the lower right are internet connectivity indicators to show what the status is of your internet connection.
When you are done distributing your media, hit the button on the lower left of the page to return to the previous screen.
iENG is designed for use by professionals and as such, assumes the users are knowledgeable in the limitations of the various services iENG will communicate with. The fact that iENG will allow you to send a 50meg HD video file via email or to Facebook does NOT mean that you should do so.
Caution, common sense, and responsibility need to prevail.
The training wheels have been removed in iENG so that professionals can benefit from the full functionality available and not be stymied by limitations imposed so idiots can survive.