The sentence starts with "He." That roughly translates to the English meaning of "is a" or "has a" - depending on context. Here, he 'ehā huina... os a clarification, with the 'ehā meaning four' which replaces the default "a". So a little more literal of a translation might be "Has 4 angles, a/the square."
Literal can be a problem when translating from a language outside a language family. So here, the Oceanic family is more contextual, and perhaps less "literal" in a English sense. Ke/ka are noun markers. They are not exclusively "a/the" as found in English. They may translate that way in some sentences, but not others. The "He" at the beginning is a different sentence structure than a "'O" at the beginning. Or an "Aia." They each have patterns. Pair that with ke/ka letting you know that the next word is a noun, and you will find that the thought being expressed does not always need "a/the." And sometimes to make it flow in English, we might add in "a/the" while it still isn't doing that function in Hawaiian. One thing I think about is with so few words in the language compared to English, many words have multiple meanings AND function as various parts of speech. One example - Ua at the beginning before a verb makes it past tense (or a completed act.) Ua after the noun indicator (ka) means rain. Sometimes it might flow to say "the rain" in English, but sometimes even in English "the" is omitted. So in translating, we might not include "the" even tho "ka" is always there, telling you it's a noun.