What are prepositional pronouns? Nothing really complicated. In all romance languages special pronouns are to be used after prepositions.
Ti vedo. I see you.
Sono partito senza te.
We already know the personal pronoun ti. What we have not seen until now is te. Te is prepositional pronoun, is used together with a preposition. The name prepositional pronoun (only used in English) is a good name for that because it points to the main function of this kind of pronoun. Nevertheless in romance languages it is called tonic pronoun (pronomi tonici). The word tonici emphasizes the fact that the pronomi tonici are pronounced more markedly than the pronomi atonici (the pronouns we already now). But it is not really important that we know how they are called, the important thing is to know when they were used. In
English there is no difference between the prepositional pronouns and the normal pronouns, in other words, the personal pronouns are used as nominative, accusative, dative and after prepositions. Easier: Prepositional pronouns don't exist in English.