What does -là at the end of the words mean?
Their meaning is similar to the one of this (-ci) and that (-là) in English. Note that it's optional, so that ce chat is perfectly valid. Usually it implies this cat rather than that cat, which is why you'll less often see the -ci ending than the -là one, unless there's a need to differentiate.
If there is no noun following this or that, you'll just translate with ceci or cela (often shortened to ça). This one or that one translate to celui-ci or celui-là.