These are prepositions. . . . We use 'in' when we refer to something, or someone being inside something. "I am sitting in the car", "My books are in my bag", "My teeth are in my mouth" "Texas is in the U.S.A". We use 'on' when we refer to someone, or something being on top, or on the surface of something, or someone. "My hair is on my head". "My glasses are on my face", "My phone is on the table", "Neil Armstrong was on the moon". We use 'at' when we refer to someone or something being in a certain position, or a certain time. "I will meet you at 9pm", "The police officer shot at the guy". I hope this helps.

just reading English books and listening to English conversations as much as you can