And what does it mean not literally?
"I'm counting on you."
I don't understand the English expression either
Well, the course assumes that learners speak English :)
Try this definition from a learner's dictionary: https://www.oxfordlearnersdictionaries.com/definition/english/count-on
Or this one from a regular English dictionary: https://dictionary.cambridge.org/dictionary/english/count-on-someone-something
No, it means something different. "I count with you" would mean something like "I matter to you." It sounds a bit awkward, though someone might ask "Do I even count with you?" (Or it could also mean, "You and I are counting together, 1 2 3 4 5...")
"I am counting on you" is a pretty common expression, meaning that I am relying on you for something in particular. "I count on you" means that I habitually rely on you.