Go to APPS>ANNOUNCEMENTS
Click the announcement you want to add a gallery to.
Click inside the announcement description box where you want the gallery to go.
Click on INSERT IMAGE / DOCUMENT button in WYSIWYG toolbar.
Click on the ADD NEW FOLDER button and give your folder a name, then click CREATE.
Click on the new album you just made to open it. Upload your images into that folder by dragging them directly into the media box there or clicking the UPLOAD FILES link at the top left of the media window you are in and clicking the SELECT FILES button.
Once the images are uploaded, click on CREATE GALLERY > MENU at the very top of the media box and then choose CREATE GALLERY.
All the images should have a check on them since you just uploaded them.
If so, click the blue CREATE A NEW GALLERY button at the bottom right of the media box.
In the LINK TO dropdown in the grey panel that comes out on the right of the screen, choose MEDIA FILE. You can leave everything else the same.
Click INSERT GALLERY button at bottom right of the media box.