Primarily a Dative preposition, "zu" is used to indicate direction or purpose. When discussing directions, "zu" directs us towards destinations that are not necessarily enclosed spaces or specific points. For example, "Ich gehe zu meinem Freund" means "I am going to my friend's place," and "Er fährt zur Arbeit" indicates "He drives to work." For visiting people, "zu" is preferred, as seen in "Ich gehe zu meiner Mutter" ("I am going to my mother").
Additionally, "zu" is used when attending events or participating in activities, such as "Wir gehen zur Party" ("We are going to the party") and "Er kommt zum Treffen" ("He is coming to the meeting").
Comparatively, the preposition "in" is used for enclosed spaces or countries and also takes the Dative case. For example, "Ich bin in der Stadt" means "I am in the city," and "Er ist in der Schule" translates to "He is in the school." When the location is inside a bounded area, "in" is appropriate, as in "Sie ist im Park" ("She is in the park").
On the other hand, "auf" is used for open spaces, surfaces, or places where an activity is performed, and also uses the Dative case. Examples include "Die Bücher liegen auf dem Tisch" ("The books are on the table") and "Wir sind auf dem Markt" ("We are at the market"). "Auf" is particularly useful for places like markets, islands, or events held in open spaces, such as "Er ist auf der Insel" ("He is on the island") and "Wir sind auf der Veranstaltung" ("We are at the event").