what is the difference between voda/vodu? and kava/kavu?
One is nominative, the other is accusative. Czech nouns use grammatical cases, check the lecture notes.
Names should not be test in the App. Matěj, for example, is either Matt or Matthew in English. However, the App incorrectly marks translation of names when it should focus only on sentence structure. It should not be about spelling names.
Do not translate names. Ever. Just don't. Matěj is Matěj and Matěj only. It is as simple as that.
But there is no facility in this test to enter letters with accents!
We always add non-accented names to English sentences. If that is not accepted, use the report button. When discussing here, mention the complete sentence that was not accepted.
This says almost the same as "Matěj má velká žizeň", doesn't it?
Firstly, velkou žízeň. Secondly, no-one said what does he need it for.
Oh, so need doesn't stand for a need to consume only
Here we have just "Matěj needs water.". It could be for anything. Washing something, extinguishing a fire, diluting something etc.