-ci and -là can be added after a form of celui to distinguish between people or objects that are closer (celle-ci) or farther (celui-là)
A form of celui can also be followed by a relative clause to mean the one(s) that or the one(s) whose
A prepositional phrase can also follow a demonstrative pronoun
Adjectives that modify forms of celui must agree in gender and number
You can use celui-là/celle-là to refer to someone in a familiar or scornful manner
Ceci & cela are also demonstrative pronouns. Unlike other pronouns, they do not refer to any noun in particular, but rather an idea. Ceci=about to be said, cela=already been said
Ceci & cela have a literary tone to them. In everyday French, use ce or ça