left panel

From top to bottom:

Import images from the filesystem or a connected camera.
Filter the images displayed in the lighttable center panel – also used to control the images displayed in the filmstrip modules.
recently used collections
View recently used collections of images.
image information
Display image information.
lua scripts installer (optional)
Install lua scripts.

right panel

From top to bottom:

Select images in the lighttable using simple criteria.
selected images(s)
Perform actions on selected images.
history stack
Manipulate the history stack of selected images.
Store an image’s history stack as a named style and apply it to other images.
metadata editor
Edit metadata for selected images.
Tag selected images.
Import and apply GPX track data to selected images.
Export selected images to local files or external services.

bottom panel

From left to right:

star ratings
Apply star ratings to images.
color labels
Apply color labels to images.
mode selector
Choose a lighttable mode.
Adjust the size of thumbnails.
enable focus-peaking mode
Highlight the parts of the image that are in focus.
set display profile
Set the display profile of your monitor(s).