Amy.G said:
I am just beginning to learn about Calvinism so forgive my ignorance.

If God has already chosen those who will be saved, what does John 3:16 mean?
I would always point people to Gill if they want a sound Calvinist interpretation of a Scripture verse. In his book
The Cause of God and Truth he exegetes a number of texts.
From His commentary:
Ver. 15. That whosoever believeth in him,.... Whether Jew or Gentile, a greater, or a lesser sinner, and of whatsoever state and condition, age or sex; and though ever so weak a believer, provided his faith, is of the right kind: not an historical or temporary one, a mere assent to the truth of things respecting his person, office, and work; but such a faith, by which a soul sees a glory, fulness, and suitableness in him as a Saviour; goes to him, ventures on him, commits itself to him, lays hold on him, and receives him, leans and relies upon him, and trusts in him, and lives upon him; and which is the faith of God's elect; a gift of his grace, and the operation of his Spirit; and which works by love, and is attended with the fruits of righteousness: now the end of Christ's crucifixion and death is, that such an one
should not perish; though he is in a lost and perishing condition in Adam, and by nature, and sees himself to be so, and comes to Christ as such; and though his frames and comforts are perishing, and he sometimes fears he shall be utterly lost; and though he is subject to slips and falls, and great spiritual decays; and shall perish as to the outward man by death; yet he shall never perish eternally, or be punished with everlasting destruction, as the wicked will:
but have eternal life; not by his works, but as the gift of God: and which he that truly believes; has already in the covenant of grace, in Christ his head, in faith and hope; and has the earnest and pledge of it, the Spirit of God; and the beginning of it, which is the knowledge of God in Christ; and shall hereafter possess it fully, and in person, to all eternity: even a life of perfect holiness and knowledge; a life of never ending pleasure; a life free from all the sorrows, distresses, and imperfections of this; and which will always continue.
Ver. 16. For God so loved the world,.... The Persic version reads "men": but not every man in the world is here meant, or all the individuals of human nature; for all are not the objects of God's special love, which is here designed, as appears from the instance and evidence of it, the gift of his Son: nor is Christ God's gift to every one; for to whomsoever he gives his Son, he gives all things freely with him; which is not the case of every man. Nor is human nature here intended, in opposition to, and distinction from, the angelic nature; for though God has showed a regard to fallen men, and not to fallen angels, and has provided a Saviour for the one, and not for the other; and Christ has assumed the nature of men, and not angels; yet not for the sake of all men, but the spiritual seed of Abraham; and besides, it will not be easily proved, that human nature is ever called the world: nor is the whole body of the chosen ones, as consisting of Jews and Gentiles, here designed; for though these are called the world, Joh 6:33; and are the objects of God's special love, and to them Christ is given, and they are brought to believe in him, and shall never perish, but shall be saved with an everlasting salvation; yet rather the Gentiles particularly, and God's elect among them, are meant; who are often called "the world", and "the whole world", and "the nations of the world", as distinct from the Jews; see Ro 11:12, compared with Mt 6:32. The Jews had the same distinction we have now, the church and the world; the former they took to themselves, and the latter they gave to all the nations around: hence we often meet with this distinction, Israel, and the nations of the world; on those words,
""let them bring forth their witness", that they may be justified, Isa 43:9 (say {b} the doctors) these are Israel; "or let them hear and say it is truth", these are "the nations of the world".''
And again {c}, "the holy, blessed God said to Israel, when I judge Israel, I do not judge them as "the nations of the world":'' and so in a multitude of places: and it should be observed, that our Lord was now discoursing with a Jewish Rabbi, and that he is opposing a commonly received notion of theirs, that when the Messiah came, the Gentiles should have no benefit or advantage by him, only the Israelites; so far should they be from it, that, according to their sense, the most dreadful judgments, calamities, and curses, should befall them; yea, hell and eternal damnation. "There is a place (they say {d},) the name of which is "Hadrach", Zec 9:1. This is the King Messiah, who is, Krw x, "sharp and tender"; sharp to "the nations", and tender to "Israel".''
And so of the "sun of righteousness", in Mal 4:2, they say {e}, "there is healing for the Israelites in it: but the idolatrous nations shall be burnt by it.'' And that {f} "there is mercy for Israel, but judgment for the rest of the nations.'' And on those words in Isa 21:12, "the morning cometh", and also the night, they observe {g}, "the morning is for the righteous, and the night for the wicked; the morning is for Israel, and the night for "the nations of the world".'' And again {h}, "in the time to come, (the times of the Messiah,) the holy, blessed God will bring "darkness" upon "the nations", and will enlighten Israel, as it is said, Isa 60:2.''
Once more {i}, "in the time to come, the holy, blessed God will bring the nations of the world, and will cast them into the midst of hell under the Israelites, as it is said, Isa 43:3.'' To which may be added that denunciation of theirs {k} "woe to the nations of the world, who perish, and they know not that they perish: in the time that the sanctuary was standing, the altar atoned for them; but now who shall atone for them?'' Now, in opposition to such a notion, our Lord addresses this Jew; and it is as if he had said, you Rabbins say, that when the Messiah comes, only the Israelites, the peculiar favourites of God, shall share in the blessings that come by, and with him; and that the Gentiles shall reap no advantage by him, being hated of God, and rejected of him: but I tell you, God has so loved the Gentiles, as well as the Jews,
that he gave his only begotten Son; to, and for them, as well as for the Jews; to be a covenant of the people, the Gentiles, the Saviour of them, and a sacrifice for them; a gift which is a sufficient evidence of his love to them; it being a large and comprehensive one, an irreversible and unspeakable one; no other than his own Son by nature, of the same essence, perfections, and glory with him; begotten by him in a way inconceivable and expressible by mortals; and his only begotten one; the object of his love and delight, and in whom he is ever well pleased; and yet, such is his love to the Gentiles, as well as Jews, that he has given him, in human nature, up, into the hands of men, and of justice, and to death itself:
that whosoever believeth in him, whether Jew or Gentile,
should not perish, but have everlasting life; See Gill on "Joh 3:15".