Nouns

The prepositional case is used only for the object of a sentence. It indicates that a sentence's object is a location or an activity.

In general, you add е (pronounced "yeh") to end of a noun. E.g., "I live in Michigan" becomes "I live in Michiganyeh."

If the noun ends in й, а, or я, replace that letter with е. E.g., "She is going to Minnesota" becomes "She is going to Minnesotyeh."

Exceptions:

Never write ие, instead write ии (Russians pronounce both, like "ee-ee").
The other exception is foreign nouns ending in о, и, or у. These look the same as the nominative case. E.g., Colorado, Kentucky, and Peru don't change.

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Plural nouns

Plural nouns in the prepositional case usually end in ах (pronounced "ach"). The ending is ях (pronounced ("yach") for soft-ending (й or ь) nouns.

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Signal words

The prepositional case is always preceded by one of four Russian words, which translate into two English words:

"In" translates to в (pronounced "veh" or pronounced with the next word if it starts with a vowel, e.g., "in Atlanta" would be "vatlanta") if the location is static. "In" translates to на (pronounced "na") for activities, or a location where an activity is done (for example, the ballet).
"About" translated to о (pronounced "oh"), or, if the following word starts with a vowel, об (pronounced "ob").

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Куда vs. где

Куда asks "where are you/he/she/etc. going?" куда asks about moving objects. It's pronounced "kooda," which sounds like a form of head lice.

Где asks "where are you/he/she/etc.?" где asks about static objects. It's pronounced "gde," like Australians saying "G'day!"

Statements that could answer the question куда are in the accusative case. E.g., "We're driving to St. Petersburg, Florida" would be in the accusative case, if you said it in Russian.

Statements that could answer the question где are in the prepositional case. E.g., "We live in Moscow, Idaho" would be in the prepositional case.

This is easy to remember because the vowels in Куда are у and а—nouns that end in а (feminine nouns) change to у in the accusative case. The vowel in где is е, the letter you add to end nouns in the prepositional case.

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Adjectives

Adjectives modifying prepositional case masculine and neuter nouns usually end in ом. For adjectives with "soft endings" (й or ь) or for the 5-letter spelling rule, the ending is ем.

Adjectives modifying prepositional case feminine nouns usually end in ой (pronounced "oy"). For adjectives with "soft endings" (й or ь) or for the 5-letter spelling rule, the ending is ей (pronounced ("yay").

Adjectives modifying prepositional case plural nouns usually end in ых (pronounced "ihch"). For adjectives with "soft endings" (й or ь) or for the 7-letter spelling rule, the ending is их (pronounced ("eehch"). As a memory aid, remember ах ых as the endings for prepositional case adjectives and nouns.

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Personal Pronouns

Я читаю о них. "I read about them." Prepositional case personal pronouns (and question words) are always preceded by о (about). In other

English	Nominative	Prepositional	Genitive
what	что ("shto")	о чём (about what? "o chyom")
who	кто ("keh-to")	о ком (about who? "o kom")	у кого (who has? "oo kovo")
I	Я ("yah")	oбо мне (about me, "o mnyeh")	у меня (I have, "oo mnyah")
you (informal)	ты ("tee")	о тебе (about you, "o tyehbyeh")	у тебя (you have, "oo tyehbyah")
he	он ("on")	о нём (about him, "o nyom")	у него (he has, "oo nyeh-vo")
she	она ("ona")	о ней (about her, "o nyay")	у неё (she has, "oo nyeh-yo")
we	мы ("mee")	о нас (about us, "o nas")	у нас (we have, "oo nas")
you (form. plur.)	вы ("vee")	о вас (about y'all, "o vas")	у вас (you have, "oo vas")
they	они ("onee")	о них (about them, "o neech")	у них (they have, "oo neech")

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Possessive Pronouns

English	Masculine	Feminine	Neuter	Plural
Whose?	чьём ("che-yom")	чьей ("che-yay")	чьём ("che-yom")	чьих ("che-eehch")
My	моём ("mo-yom")	моей ("mo-yay")	моём("mo-yom")	моих ("mo-eehch")
Your (informal)	твоём ("tvo-yom")	твоей ("tvo-yay")	твоём ("tvo-yom")	твоих ("tvo-eehch")
His	его ("yehvo")	его ("yehvo")	его ("yehvo")	его ("yehvo")
Her	её ("yeh-yo")	её ("yeh-yo")	её ("yeh-yo")	её ("yeh-yo")
Our	нашем ("nash-em")	нашей ("nash-ay") (ш is always HARD)	нашем ("nash-em")	наших ("nash-eehch")
Your (form. plur.)	вашем ("vash-em")	вашей ("vash-yay")	вашем ("vash-yem")	ваших ("vash-eehch")
Their	их ("eehch")	их ("eehch")	их ("eehch")	их ("eehch")