It is a grammatical case no5 (narzędnik), that among other
is used after jestem (I am), zostałem (I became), interesuję się (I am interested in)
is used to indicate tools used while doing something
Jadą samochodem / they go by car
Tnę to nożyczkami/I am cutting it with scissors
is used after z(ze) when it translates to with
Idę z tobą/ I walk with you
is used after pod, nad, za when action is static
In Polish language nouns, adjectives and pronouns change according to the role they play in a sentence, or after specific verb and/or preposition.
There are seven cases, which means any noun has 7x2 variants, 7 singular, 7 plural ( often they look the same but you must know which noun has which cases equal) Cases in Polish amean the ending of the noun changes.
jestem+ noun use Instrumental case.
Instrumental from mężczyzna(singular =man) -> mężczyzną mężczyźni(plural=men)-> mężczyznami
You're right, the notes ran out before the first checkpoint. I've got on through another 20 or so lessons and haven't seen one tip or note yet. I guess that's why its a Beta product. Having said that, I'm glad its out there and I'm glad they didnt wait until it was all singing all dancing as then I couldn't be having as much fun with it as I'm having now...
Now that I've got a grammar book I'm back revising all this stuff and trying to work out why everything is the way it is. Its a good strategy for me because the grammar book is short on exercises.