Blocks are items which may be added to the left, right or centre column (depending upon your theme) of any page in Moodle.
Any block can be made 'sticky' so that it appears in all the contexts below, such as throughout a course or a particular activity - see Block settings.
Blocks can be placed on the side of the screen (if your theme supports it) via the Dock icons ( and ).
Available blocks include:
There are also many contributed blocks available for download from the plugins database.