Got it! Thanks.
So -me- is the tense marker for the Present Perfect.
Although this helps to understand the difference between -na- and -me-, it doesn't answer @Jb11131999 question, which is about noun classes. Also the two sentences "You have put on." and "You are wearing." are not necessarily interchangeable although I see why you thought so.
It may get confusing sometimes, this is not an easy language. I'm also struggling with Swahili, and English grammar isn't helping either :D
Please see the comments on this in the current thread (ignoring the ones about noun class of "shati").
As Meinomiswuascht explains (in more detail):
"kuvaa" = to put on;
"unavaa" = you are putting on;
"umevaa" = you have put on = you are wearing.
(This is standard Swahili, not a Kenyan variant.)
Shati = Ma class (I really do not know about other clothes, maybe n class: kofia, kanzu = N class)
Karibu rafiki! I find this page very useful, and I have just added the conjugation chart for this verb (-vaa):
There are two conjugation charts (affirmative and negative) to find the progressive, perfect, past, future (for indicative) between other conjugations. :)
Also, I share some videos explaining the use of "me" here (with perfect tense and statives):
I found this document https://www2.ku.edu/~kiswahili/pdfs/Lesson_09.pdf, which says that the N-N noun class has many English borrowings, but I didn't find "shati" in it. It also says that the borrowings in this class have the same form in singular and plural, but "shati" in the plural is "mashati", so now I'm a bit confused about it. Since "nzuri" was changed to "zuri", it leads me to believe that it is the "ji" noun class according to this other document: https://www2.ku.edu/~kiswahili/pdfs/lesson_24.pdf
I'll keep looking for a definite answer, in the meantime if you find it, let me know, ok?
With borrowed words, it tends to be that the Kiswahili grammar won't always transfer. So growing up in a Swahili speaking family, we've used both "shati" and "mashati" to both mean "shirts". A good example of a borrowed word that doesn't necessarily follow the rules in "Chapati". Chapati is a word borrowed from India, it's a type of flatbread. Since it starts with a "ch-" the natural inclination for the plural would be "Vyapati" but saying "Chapati" and meaning plural is also acceptable.
Also to address the "nzuri" question. Since "nzuri" is an adjective you conjugate it to first the noun. You do this by dropping the "n" and replacing it with the same prefix of the noun class of the noun.
"nice trees" would be "miti mizuri"
"nice tree" would be "mti mzuri"
"nice chairs" would be "viti vizuri"
"nice chair" would be "kiti kizuri"
There are exceptions such as: "nice ocean/sea" -- "bahari nzuri"
But those will be learned over time and as you get more advanced in Kiswahili.
I can't remember where I read it now, but I think I read that loan words used to most commonly go into the MA class but these days it's more common for them to go into the N-class, so older borrowings are often in the MA class.
Also, there seems to be some degree of flexibility between these two classes in particular. Dictionaries usually list words such as rafiki as belonging to both classes. From googling phrases in quotes such as "rafiki wangu" vs "rafiki yangu", "marafiki wangu" vs "rafiki zangu", it looks like it belongs to the N-class much more often.
(This wouldn't work with adjectives since adjectives for animate nouns always take the M-WA class concords, but possessives in the N-class do not.)
In any case, if in doubt, I tend to guess that animate nouns (referring to people and animals) that have no obvious class marker belong to the N class and inanimate nouns with no obvious marker belong to the MA class and I think I get it right more often than not.
And at the end of the day, most users of Swahili are also not native speakers, so I can't imagine anyone would really laugh at you for saying "shati nzuri" instead of "shati zuri" or "shati yangu" instead of "shati langu".