Russian has one word for both "butter" and "oil". The context should help you differentiate between the two in real life. For example, liquid масло is poured, so if you hear someone saying something like "Налей масло в салат." you'd know that they're talking about oil. Solid масло is 'put/placed', so if someone says something like "Положи масло в картошку." they're obviously talking about butter. Also, oil is often talked about with an adjective in front of it, such as: оливковое, подсолнечное.... (olive, sunflower etc.). Hope this clarifies it for you :)
Everything is my in English. But Russian is a language with grammatical gender, nouns can be masculine, feminine (regularly ending with -а) or neuter (regularly ending with -о), and you need need to distinguish between singular and plural.
- my brother: мой брат
- my sister: моя сестра
- my butter: моё масло
- my cars: мои машины