In Russian, there are two really important cases called the instrumental case and the locative case. They help us understand different things in a sentence.

1. Instrumental Case:

• What it does: This case shows how something is done or what is involved in an action.
• Example: Я пишу ручкой. (This means, "I am writing with a pen.")
• How it looks: In this case, masculine nouns usually end in -ом, and feminine nouns often end in -ой.

2. Locative Case:

• What it does: This case talks about where something is or when it happens.
• Example: Я живу в Москве. (This means, "I live in Moscow.")
• Common words used with it: You often see this case with the words “в” (which means "in") and "на" (which means "on").

Summary: Use the instrumental case to explain how something happens.
Use the locative case to tell where something is or when it happens.