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We believe in one God
This is key -- we are monotheist, we do not believe in multiple gods

, the Father Almighty, maker of heaven and earth, and of all things seen and unseen.
God created the world -- there was no demiurge like the Gnostics believed

And in one Lord Jesus Christ, the only begotten Son of God, and born of the Father before all ages.
defining who Jesus was/is/will forever be
God from God, Light from light, true God from true God. Begotten not made, consubstantial to the Father, by whom all things were made.
Jesus is of one being with the Father, not a separate god, not a created being, not a sub-god or godling
Who for us men and for our salvation came down from heaven. And was incarnate of the Holy Ghost and of the Virgin Mary and was made man; was crucified also for us under Pontius Pilate, suffered and was buried; and the third day rose again according to the Scriptures.
Jesus' life here on earth -- key "according to Scriptures"

And ascended into heaven, sits at the right hand of the Father, and shall come again with glory to judge the living and the dead, of whose Kingdom there shall be no end.
there is no end to His Kingdom

We believe in the Holy Spirit, the Lord and Giver of life, who proceeds from the Father , who together with the Father and the Son is to be adored and glorified, who spoke by the Prophets.
Definition of the Holy Spirit

And one holy, catholic, and apostolic Church.

We confess one baptism for the remission of sins, the resurrection of the dead and the life of the world to come.

In Latin

Credo in unum Deum,
Patrem omnipoténtem,
Factórem cæli et terræ,
Visibílium ómnium et invisibílium.
Et in unum Dóminum Iesum Christum,
Fílium Dei Unigénitum,
Et ex Patre natum ante ómnia sæcula.
Deum de Deo, lumen de lúmine, Deum verum de Deo vero,
Génitum, non factum, consubstantiálem Patri:
Per quem ómnia facta sunt.
Qui propter nos hómines et propter nostram salútem
Descéndit de cælis.
Et incarnátus est de Spíritu Sancto
Ex María Vírgine, et homo factus est.
Crucifíxus étiam pro nobis sub Póntio Piláto;
Passus, et sepúltus est,
Et resurréxit tértia die, secúndum Scriptúras,
Et ascéndit in cælum, sedet ad déxteram Patris.
Et íterum ventúrus est cum glória,
Iudicáre vivos et mórtuos,
Cuius regni non erit finis.
Et in Spíritum Sanctum, Dóminum et vivificántem:
Qui ex Patre procédit.
Qui cum Patre et Fílio simul adorátur et conglorificátur:
Qui locútus est per prophétas.
Et unam, sanctam, cathólicam et apostólicam Ecclésiam.
Confíteor unum baptísma in remissiónem peccatorum.
Et expecto resurrectionem mortuorum,
Et vitam ventúri sæculi. Amen

The Athanasian is even more explicit in defining the nature of the Godhead:

we worship one God in Trinity, and Trinity in Unity; Neither confounding the Persons; nor dividing the Essence.

For there is one Person of the Father; another of the Son; and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one; the Glory equal, the Majesty coeternal.

Such as the Father is; such is the Son; and such is the Holy Ghost.

The Father uncreated; the Son uncreated; and the Holy Ghost uncreated.

The Father unlimited; the Son unlimited; and the Holy Ghost unlimited.

The Father eternal; the Son eternal; and the Holy Ghost eternal.

And yet they are not three eternals; but one eternal.

As also there are not three uncreated; nor three infinites, but one uncreated; and one infinite.

So likewise the Father is Almighty; the Son Almighty; and the Holy Ghost Almighty. And yet they are not three Almighties; but one Almighty.

So the Father is God; the Son is God; and the Holy Ghost is God. And yet they are not three Gods; but one God.

So likewise the Father is Lord; the Son Lord; and the Holy Ghost Lord. And yet not three Lords; but one Lord.

For like as we are compelled by the Christian verity; to acknowledge every Person by himself to be God and Lord; So are we forbidden by the Catholic Religion; to say, There are three Gods, or three Lords.

The Father is made of none; neither created, nor begotten. The Son is of the Father alone; not made, nor created; but begotten. The Holy Ghost is of the Father and of the Son; neither made, nor created, nor begotten; but proceeding.

So there is one Father, not three Fathers; one Son, not three Sons; one Holy Ghost, not three Holy Ghosts.

And in this Trinity none is before, or after another; none is greater, or less than another.

But the whole three Persons are coeternal, and coequal. So that in all things, as aforesaid; the Unity in Trinity, and the Trinity in Unity, is to be worshipped. He therefore that will be saved, let him thus think of the Trinity.

Furthermore it is necessary to everlasting salvation; that he also believe faithfully the Incarnation of our Lord Jesus Christ.

For the right Faith is, that we believe and confess; that our Lord Jesus Christ, the Son of God, is God and Man; God, of the Essence of the Father; begotten before the worlds; and Man, of the Essence of his Mother, born in the world. Perfect God; and perfect Man, of a reasonable soul and human flesh subsisting.

Equal to the Father, as touching his Godhead; and inferior to the Father as touching his Manhood.

Who although he is God and Man; yet he is not two, but one Christ. One; not by conversion of the Godhead into flesh; but by assumption of the Manhood into God. One altogether; not by confusion of Essence; but by unity of Person.

For as the reasonable soul and flesh is one man; so God and Man is one Christ; Who suffered for our salvation; descended into hell; rose again the third day from the dead. He ascended into heaven, he sitteth on the right hand of the God the Father Almighty, from whence he will come to judge the quick and the dead.