In the File Manager's right pane, do one of the following:
To select a single file/folder, click on the file/folder's row.
To select multiple files, press and hold the CTRL key, while clicking on the desired files or folders.
To select all items in the current folder, click Actions and then click Select All, or press CTRL+A.
To select a range of files, press and hold the Shift key, click the file at the start of the range, and then click on the file at the end of the range.