flightless fruit flies are fine to feed baby crested geckos, though it is better to start them on the crested gecko diet.
To post pictures, first you have to upload the pictures to a image hosting website (the kingsnake gallery is perfect) Once you have the pictures on a webpage, if it's kingsnake, you can just choose it from the available images list located at teh bottom of the 'new message/post' screen. Or, if you use another picture hosting site (or website) you can copy the URL (webaddress) to the actual picture you want to show into the body of your message, but enclose the link with img at the start and /img at the end, both enclosed by [].
There is also a link in the lower right corner of the message area called Tools and Toys which gives you some more details of what you can do in your messages.