Marzec to miesiąc roku??
It's clever how 'roku' gives away that the previous information falls on it by its locative case. Inflected languages really do fit together like clockwork
When do you use 'miesia' or miesiacem for month? I thought it was miesia with the negative 'nie' but that is not true in this statement. Very confusd.
Both sentences are correct because they have the same meaning:
March is a month - Marzec to (jest) miesiąc/ Marzec jest miesiącem
March is NOT a month - Marzec to NIE miesiąc/ Marzec NIE jest miesiącem
Why is no preposition necessary before roku to signify "of the"?
That's what the genitive case (rok -> roku) is for.
Why is it marzec? Why not marsz?
Because "marsz" is when you're marching ;)
I enjoy gratitude for Duolingo, but is this really a useful sentence for conversations (when lockdown eventually allows me back to my beloved Hamsa courtyard cafe) ?
No, some vocabulary has clearly been introduced too early to make it possible to create meaningful sentences. This is one of examples, this sentence is far from great.