Objects can be discovered using the Discovery Tool. They are found in the Objects category in the Discovery Menu. Once discovered, most Objects must then be unlocked before they can be placed freely. The majority of objects cost 250 Studs to unlock, though some can range much higher (up to 10,000 or more!).
As of Update 1, there were 191 props available to collect and unlock.
As of LEGO Worlds full release (7 March 2017) there were over 600 props, and that number continues to increase with each new update and DLC release.
Some Objects (especially those that are part of a Brick Build) can be interactive when placed.
Objects drop Studs when destroyed or interacted with.
Title Update 3 introduced new categories for everything, including Objects. When selecting "Categories" from the appropriate part of the Discovery Menu, they will be displayed in traditional LEGO Bins, as follows (click on the bin to see the Objects inside!):