Translation:This is fish, but I do not eat soup with fish.
F: Це риба. (This is fish). Ця риба (this fish)
M: Це кіт. (This is a cat). Цей кіт (this cat)
N: Це молоко. (This is milk). Це молоко (this milk) <-- THE TRICKY BIT
You are partly right :) It still works with "fish" in this case, but they do clash with neuter.
'This is fish' is «це риба», here це is an noun-like pronoun that doesn't change its form.
'This fish' is «ця риба», here ця is an adjective-like pronoun that changes its form according to the form of the noun it modifies (here it has a feminine form, ця, because ри́ба is feminine). Masculine form is 'цей', neuter is 'це'.
The confusion can arise only with neuter nouns: це ві́кно can mean either 'this window' or 'this is window'. With neuter nouns, you can distinguish the two meanings only be context and by intonation.
Yes, this is correct!
You can find tips like these in every lesson though, if you don't want to be guessing all the time:
You click on the "ball" first and then on the lamp symbol, and this will pop up.
Yes, the default meaning of "X with Y" in food is "Y X" in English :D E.g. Суп з рибою = fish soup, салат з помідорами = tomato salad.
In some cases it's possible to say "Y (adjective) X" instead of "X with Y" e.g. рибний суп = суп з рибою. Sometimes there's a slight difference e.g. грибний суп = mushroom soup, суп з грибами = soup that has mushrooms in it (but maybe it's a fish soup, just also with mushrooms).
It's very seldom that "X with Y" means separate things, e.g. soup and fish, not fish soup. As far as I know nobody says "X with Y" in that case, they would say "X and Y".
In case X and Y are not "mixable" (it's not a soup or a salad etc.), then "X with Y" just means "X and Y" e.g. Я їм рибу з помідорами = I'm eating fish with tomatoes, not a dish, just eating fish and tomatoes.