That questions a bit open Max and your basically asking someone to write you a script for a gallery. If you are truly interested in learning as3, you need to break your questions down.
If your gallery needs to load photos then it may well need to be dynamic and use xml.
Most of us have all been where you are now. one step at a time!
personally I would find out how many images need to be loaded, load the urls in to an array.

then a for statement that runs through that array, have a movieclip in your library set to "export" this allows you to load mc's from the libary using code, then I would load that image in to the movieclip and increment the each movieclips x and y.


you should make a start with where you want your images to come from. Outside or inside of flash.