my purpose of exporting (for the time being) are:
1) to be able to view full-screen on a monitor in widescreen and be able to save in a thumbdrive & let my sister watch it in her computer
2) to be able to post in facebook
For watching fullscreen on the computers, export as a self-contained Quicktime Movie. For exporting to Facebook, export using Quicktime Conversion.
after exporting using QuickTime Movie, how to I check the anamorphic flag to see it in widescreen (since the link says Exporting to QuickTime movie is in 4:3) ?
The anamorphic flag is in a column of your browser or in Item Properties for the clip. All clips should be marked as such as anamorphic before editing. You click the part in Item properties or the browser for the clip next to anamorphic to flag it. You can then edit like normal and export as a normal Quicktime Movie. Quicktime Movie is not 4:3, it keeps the aspect ratio of your original video.
which option shall I choose if I wanna load it on facebook ?
From Tom's link, +"In these cases you need to export to QuickTime Conversion, setting the frame size to 853x480. This will be a 16:9 equivalent of your anamorphic material. If you need a smaller size, set the frame size to same ratio, 800x450, 720x405, 640x360, 600x338, 480x270, 320x180, or any other combination of dimensions that produces the same result."+
So, export to H.264 codec (a nice codec for web viewing) at one of these frame sizes, preferably 853x480 if you want better quality.