Russian typically expresses possession using statements of existence, i.e. "In a place X, there is an object A":
- Здесь есть масло. = There is butter here.
- В доме есть масло. = There is butter in the house.
- В доме есть пицца. = There is a pizza in the house.
- В пицце есть сыр. = There is cheese in the pizza.
- У меня есть сыр. = I have cheese.
- У папы есть пицца. = Dad has a pizza.
- У папы есть я. = Dad has me.
(it still makes sense to translate these with "have/has" because in English, have is the most common way to express possession)
You specify what kind of oil, for example "olive oil" is оливковое масло.
You can also specify butter made from cream as сливочное масло. http://dictionary.reverso.net/russian-english/%D1%81%D0%BB%D0%B8%D0%B2%D0%BE%D1%87%D0%BD%D0%BE%D0%B5
In singular nom/gen there propably isn't that much difference, since the stress is on the firs syllable. Both a and o are reduced, and although the resulting vowel isn't exactly the same, it's very close (and I suspec in some cases is the same). In plural nom/acc the stress is on the second syllable, which means the first a is reduced instead of the second.
Jonestly Russian could use some more endings for the cases :D
The singular genitive form looks like the plural nominative form. The semicolon won't let me get you to the exact page but type in папы and enter for the table. There is a genitive plural form: пап. http://starling.rinet.ru/cgi-bin/morph.cgi?flags=endnnnnproot=configword=%EF%E0%EF%FB