The particle に can be challenging for learners because it translates to several different prepositions in English. Commonly, it can mean 'in', 'at', 'to', 'for', or 'on'. Let's examine one instance of each use.

• 猫(ねこ)は箱(はこ)にいます。
  The cat is in the box. (に as 'in')
• 友達(ともだち)は駅(えき)にいます。
  My friend is at the station. (に as 'at')
• 学校(がっこう)に行(い)く。
  To go to school. (に as 'to')
• クリスマスにプレゼントをもらう。
  I get presents for Christmas. (に as 'for')
• 電車(でんしゃ)に乗(の)る。
  To get on the train. (に as 'on')

Although these different translations can seem overwhelming, it's helpful to understand に as having a single, core function. This function is to mark the 'destination' or 'end point' of a verb. This implies that the action described can only happen or be fulfilled upon reaching, or while at, the place or time indicated in the sentence.

• 京都(きょうと)に住(す)む。
  To live in Kyoto.
• ホテルに泊(と)まる。
  To stay at a hotel.

Learners are often confused by verbs such as 住(す)む (to live/reside), which take に instead of で. The reason for this also ties back to the idea of a destination. 住(す)む is an action that can only be 'fulfilled' at its location. (In other words, the act of living can only take place in the place where one lives).