The particle "に" in Japanese is used to indicate a specific point in time or a destination. For example, when saying "学校に行く" (がっこうにいく), it means "to go to school." Here, "に" shows the direction of the action. Additionally, "に" can express the purpose of an action or the target of an action. For instance, in the sentence "友達に会う" (ともだちにあう), it translates to "to meet a friend." In this case, "に" indicates the person being met.