で is one of the most common particles in Japanese. It has several core uses: it marks where an action takes place (as opposed to に, which marks where something exists), it marks the means or tool you use to do something, and it marks the language or vehicle you use. For example, ここで食べる means 'eat here', はしで食べる means 'eat with chopsticks', and 日本語で話す means 'speak in Japanese'.\n\nWhen で marks location, the verb must be an action verb (like 食べる, 勉強する, 遊ぶ). For existence verbs (いる, ある) or states, you use に instead. So you say 図書館で勉強する (study at the library) but 図書館に本がある (the book is in the library).\n\nで can also express the total number of participants or the duration when something is completed. For example, 二人で行く (go as two people) or 一時間で書く (write in one hour). But at N5, the main uses are location, means, and language.