By dropping folders onto Pix's icon in the Finder or the Thumbnails… menu command Pix is told to create thumbnails for the image files contained in the chosen folders. In case of the Thumbnails menu command the chosen folder is the folder containing the currently displyed picture or video resp. (in the search results view) the folders containing the selected thumbnails. You might experience strange effects if one of these folders contains another one, but if some folder is in the folder set chosen for the thumbnails, then it does anyway not make sense to add a subfolder of this folder, too.
Pix then opens a window with thumbnail views of these images in the preset size with the name of the respective image file written under them. The file name under the thumbnail is truncated if it does not fit into the thumbnail area. In this case the full file name is shown as a tool-tip when the cursor is moved over the file name field.
The window title is the name of the most specific folder containing the root folders, followed by the total number of thumbnails.
At the bottom of the window you will recognize a slider. This can be used to adjust the size of the thumbnails.
Thumbnails can be selected by clicking on them. By shift-clicking (i.e. clicking the mouse while the shift key is pressed) and command-clicking multiple thumbnails can be (de-)selected, like files in the Finder.
The menu command Delete moves the image files corresponding to the selected thumbnails to the trash (If the files are located on a remote computer which is accessed via file sharing, the action is somewhat different: The files are copied to the local trash and get deleted on the remote computer.) and removes these thumbnails from the view.
Double-clicking on a thumbnail opens a window displaying the image as described in the page "The Single Image View"
Hitting the 'enter' or 'return' key opens the selected images in own windows.
With the menu command Save as… pictures selected in the thumbnails view can be moved to other locations in the file system.
Image files can be moved to folders covered by the thumbnails view by selecting their symbols in the finder and dragging them into the respective section of the thumbnails view.
Hitting the space bar of the keyboard moves the visible part by one page vertically (if there is a page left over. Otherwise as much as there is left over). The direction is upwards if the shift key is pressed at the same time, otherwise downwards.
The menu command Refresh adjusts the thumbnail window to changes in the file system.