You'll need to decide whether you are using Save As or Export/Save for Web for the GIF and PNG file formats.
You'll also need to decide which options to use for each file format.
In all cases you would probably create a separate function containing the required SaveOptions for each file format. You'll also need to setup a save path and document naming and call the various functions.
It is not clear whether all three file formats should be saved each time the script is run, or whether the user is required to pick and choose combinations of the three formats.
There are many examples for saving different file formats in various forum posts, here is one example of saving PSD & JPEG versions in the same script: