M- is the subject marker for You(plural)
-na- is the tense marker which is the present tense
-pika is the verb stem, from kupika, which means to cook
What does (pl) mean?
It's short for "plural" ... they need to indicate it because aside from informal usage (which varies heavily by dialect), English has no way of distinguishing singular (sg) "you" from plural (pl) "you".
mnapika means you are cooking
unapika means i am cooking
be aware on the test out quiz it has una and mna meaning you are cooking