The Instrumental: With Milk, With Friends
Your café order — кофе с молоком — was grammar all along. The instrumental is the case of with: with what, with whom, and (surprisingly) as what and when.
с + Instrumental
чай с лимоном, кофе с молоком, хлеб с сыром
tea with lemon, coffee with milk, bread with cheese
Note: The entire café menu, correctly declined.
The opposite — без (without) — takes the genitive: кофе без сахара. With = instrumental, without = genitive.
With People Too
Я иду в кино с другом.
I'm going to the cinema with a friend.
заниматься
The activity verb takes a bare instrumental — no preposition:
You Already Speak It
Common Mistakes
- с + wrong case. С молока means "off the milk" — with is с + instrumental: с молоком.
- заниматься с спортом. No с here — the verb takes the instrumental directly: заниматься спортом.
- Missing the -ой. С мама → с мамой. Feminine -а becomes -ой.
What You Can Do Now
You can say who you spend time with, what you take in your tea, and what you practice — plus you've decoded a dozen words (зимой, вечером…) you've been using since Chapter 2.