"В" and "на" - prepositions. "В" is translated as "In, at, into, to, for". In other words it means "inside" Examples: I live in Moscow - Я живу в Москве She puts cards in the box - Она кладёт карточки в ящик He works at school - Он работает в школе Children play in the garden - Дети играют в саду She is afraid to go into the forest - Она боится войти в лес I'm going to Paris - Я собираюсь в Париж Students go to school every day - Ученики ходят в школу каждый день He left for Europe - Он уехал в Европу Professor entered the hall - Профессор вошёл в зал Young guys had entered the community - Молодые ребята вступили в сообщество "На" is translated as "on, upon". In other words it means "on the surface" Examples: Books are on the table - Книги на столе I hang this picture on the wall - Я повешу картину на стену She lives in Cyprus (simply, she lives on te surface of the island, planet,earth) - Она живёт на Кипре Planes fly to the south - Самолёты летят на юг It's noisy in the street - Шумно на улице I live in Moscow in Varvarka street - Я живу в Москве на улице Варварка "На" is also translated as "at": He is at work - Он на работе (just a fact) He went to work (with his head) - Он погрузился в работу (с головой). Simply, he went inside his work. She met a friend at a concert - она встретила друга на концерте. In other words "during the events" She is going to a concert - она собирается на концерт. Just a fact. It was fun at the wedding - Было весело на свадьбе ("during the events")

Unfortunately there are no rules and if you want to speak Russian properly you should or must learn substantives with their appropriate prepositions "в" or "на". I am a native Russian speaker but I cannot explain it to you why we say "в музее" but "на выставке", "в театре" but "на концерте". It is one of the difficulties of Russian. My native language has a lot of surprises for those who learn it.

на- when you want to say that something is on the top- на доме- on the house в- when you want to say that something is inside в доме- in the house hope it helps!