les pronoms démonstratifs

celui, celle, ceux, celles

Celui , celle, ceux, celles ('this one' or 'that one' in the singular; 'these,' 'those' or 'the ones' in the plural) are demonstrative pronouns. 

They replace a specific noun, which has been mentioned or is obvious from context, in order to avoid repeating it. They agree in gender (feminine/masculine) and number (singular/plural) with the nouns they replace.

Celui de/d', celle de/d' etc. show possession. They are generally translated by 'that' of', 'those of' or by the possessive form. 

-ci and -là are added to the demonstrative pronouns to indicate nearness or farness like the distinction between 'this one' and 'that one' in English.

Celui qui ... , celle qui ... mean 'the one that', 'the one who' and ceux qui ... , celles qui ... mean 'those that / who'.  They introduce a relative clause in which they are used as subjects. In the example below, ceux qui is the subject of the verb 'portent'.

Celui que ... and celle que ... mean 'the one that / whom / which', ceux que ... and celles que ... mean 'the ones that / whom / which'. They introduce a relative clause in which they are used as objects. In the example below, celle que is the object of 'j'aime'.

Celui dont... and celle dont...mean 'the one' whose', 'the one of which', ceux dont ... and celles dont ... mean 'those whose', 'the ones of which'. They introduce a relative clause in which the verb takes an object introduced by de (parler de, 'to talk about')

ceci, cela

Ceci (this) and cela (that) are invariable demonstrative pronouns. They refer to things that cannot have a specific gender assigned to them, like ideas or statements. Ça is used in a familiar or conversational style in place of cela for emphasis.