File > Import Image lets you select one or more graphic image files and bring them into the Springboard story file.
Supported import formats include Windows Bitmap (BMP), Encapsulated PostScript (EPS), GIF, JPEG, Photoshop (PSD), PNG, Targa (TGA), TIFF, Windows Metafile (WMF), and Enhanced Metafile (EMF). Alpha channels are supported in BMP, Photoshop, PNG, Targa, TIFF, and Metafiles; a single level of transparency is supported in GIF files.
You can select the files to import in the usual file-selection dialog.
Springboard then shows you the files in a list:

The files are in alphabetic order by default, but you may drag them up or down to reorder them.
You may also choose one of the radio buttons below the list to determine how the new images will be inserted:
When you press OK, Springboard checks the size of the input files. If some are larger than the frame size, it presents the Reduce Imported Images dialog:

Reduce is generally the right choice; it discards the resolution that is not needed to display the image at the frame size. But, you can choose Import Full-Size to keep the full resolution internally if you plan to enlarge the imported images later, or if you want import frames at the full size of the image files.
Images are imported as full-color layers. Once imported, you can optionally convert them to spot-color layers with the Image > Convert command.
Images imported as layers are automatically scaled to fit the current frame and centered. If you chose Import Full-Size, you can later restore them to their original scale with Layer > Reset Position.