To select multiple files, first click in the upper corner of a file’s thumbnail image. This will bring up the selection state with this file selected.
From here you can select multiple photos by either clicking anywhere on individual files. If you'd like to select a group of files at once please select the first file, then hold Shift on the keyboard and click another file - this is to quickly select the group of files between the two that you selected.
If you have any further questions, please don’t hesitate to email us at support@forever.com.