two: the cardinal number that counts a set of exactly two
This is simply the Hebrew word for the number two, by far the most common number word in the Old Testament after one. It counts two of anything: two animals, two stones, two sons, two years. In its plain use it works exactly like the English "two", and most of its hundreds of occurrences need no more explanation than that.
The interest lies in a handful of fixed expressions that grow naturally out of the bare count. Joined to a personal ending, it becomes "the two of them" or simply "both", drawing two people together as a single pair ("the two of them walked on together"). It names a matched set as "a pair", as in two turtledoves brought for an offering. Doubled, it gives the distributive "two by two", the picture of the animals filing into the ark. And it can mark a portion rather than a tally: "two parts" of something, which in practice means a double or larger share, as with the firstborn's inheritance or a double measure of a prophet's spirit.
These are not separate words, only the everyday flexibility of a number. A reader meets the same word each time; only the surrounding phrase decides whether it is counting, pairing, or measuring.