The instrumental case in Russian helps us show how something is done or who is with us. Let's make it easy to understand!

1. How to Form the Instrumental Case:

• For masculine nouns: Add “ом” to the end.
  (Example: "стол" becomes "столом" which means "table.")

• For feminine nouns: Add “ой” to the end.
  (So, "девушка" changes to "девушкой" which means "girl.")

• For neuter nouns: Add “ом” to the end.
  (Like "окно" turns into "окном" which means "window.")

• For plural nouns: Add “ами” to the end.
  (For example, "книги" changes to "книгами" which means "books.")

2. When to Use It:

• To show how something is done:
  “Я пишу ручкой.”
  (This means: I write with a pen.)

• To show who is with you:
  “Я иду с другом.”
  (This means: I am going with a friend.)

3. Example Sentences:

• How something is done:
  “Он учится с тетрадью.”
  (This means: He studies with a notebook.)

• Who is with you:
  “Мы гуляем с собакой.”
  (This means: We walk with a dog.)

Try practicing these forms and sentences! It will make you better at using the instrumental case in your conversations.