This game really doesn't explain how to make money or how much is rent and when you pay it. Like, I can't even interact with the rooftop, I don't know where to sell items, what to make since these things take days to grow?
Rooftop, go to your room and click the button that says the word "rooftop" in it.
Lavender and mint grow automatically daily. if you want more then click the button that says "garden" when you're on the rooftop and you can harvest any planters you have added there. You buy planters in the obvious place, the store, when you select the 'trade' button.
The game used to be hard to figure out where to sell stuff when you couldn't unlock the spa initially, but now I believe that, and the bar are unlocked first thing now.
As for it 'explaining how to sell', well click buttons, explore, it's very easily understandable if you're not waiting for it to literally tell you "step 1 is..." and step 2 is..."
As for rent, there isn't any as far as I know, if it's not mentioned as an upcoming expense and a set amount then don't worry about it.