at/in

Evo,

Prepositions are very, very tricky in English and they often seem to have few rules to help you with figuring out when to use which ones. However, there are some general guidelines.

Here are two sites that may help you:

http://owl.english.purdue.edu/handouts/esl/eslprep2.html

http://owl.english.purdue.edu/handouts/esl/eslprep.html

These both relate to places.

Don't be discouraged by these. No native speaker will misunderstand you if you say "I arrived to New York at Saturday" instead of "I arrived in New York on Saturday."

Trust me, no one will care.

Sometimes it's important - I need this report by Friday versus on Friday, but when it comes to places, no one will misunderstand. Same with "I rode on a car" (although someone may smile, picturing you gripping the roof rack as you sped down the highway). No one will misunderstand. The first goal is simply to communicate. Perfecting these little things later is fine - don't let them keep you from trying to speak.