A bit of technical stuff:

CObs have a family, genus and species number. Of the families, usually 2 (simple objects) and 3 (compound objects) are offered. Genus refers to a grouping that creatures can identify; for example, 6 (food), 7 (drink) or 14 (toy). The species number identifies different objects in a genus to the game; a creature itself cannot differentiate between cheese and carrots. The game has to, if carrots and cheese are to have different effects. If you install two CObs with the same family, genus and species numbers, conflicts will occur - getting pump water out of a donut vendor, for example.

There are only 255 different species per genus. So if someone gives their food COb a family/genus/species number of 2-6-260, the game interprets this as 2-7-5, and the norns see the COb as a drink! In CObfinder, this COb would be listed under '2-7 Drink', rather than as a food. If you're looking for a particular COb and can't find it where you think it should be, check the next couple of categories, or search through the Full Index.

To get CObs into the game, you have to use the Object Injector, by CyberLife. A range of C1-related downloads can be found on the download page of the CreaturesLabs website. Some CObs also require that you be running a patched version of the game, either 1.02 or 1.04 - again, both downloads are available from CyberLife.

A few words of warning. A badly-written COb can crash the game, although in my experience this is rare. Don't install a lot of CObs at once - do one and run the game for a while so you're certain it's OK before you add another. Also be aware that a COb that works fine on one system may cause problems on another. The CyberLife site does have a number of patches and troubleshooting documents if you get stuck. If in doubt, close the game down (which forces a save) and start the game again before adding a COb - then if the game crashes and you have to revert to the backup version, you won't have lost much. Also be aware that some CObs, such as the Beelacanth plants, shiitake mushroom logs and zinger butterflies, affect system performance; in general, any COb running a lot of scripts, or scripts using the timer, should be used sparingly. A backlog of scripts waiting to be run produces the interesting "egg in the sky" effect. You'll know it when your norns see it.