Since you have been away for a long time…perhaps “focus” more on any mortal sins you have done in life for this first confession (venial sins need not be directly confessed…though it is recommended we do so regularly…one can intend the other venial sins in “and all the sins of my life” at the end).
We are obliged to confess all mortal sins in number and kind (adultery 2x, murder 4x, missing Mass all Sundays and Holy Days except Christmas for the last 5 years, perjury in court 2x, receiving Communion while in state of Mortal sin 2x, etc etc) and if something changed the mortal sin…like it was your brother you murdered. Of course after a good examination we may not …after so many years…remember everything…that is ok…we do what we can…God forgives the forgotten ones too (we need of course to be sorry for all our mortal sins…and amended)…then if we later remember one we forgot…we are to confess it in the next confession after we remember it. (this is different from if we intentionally hide a mortal sin…that is a sacrilege and one is not forgiven but has another sin)
Also we may not know the numbers …we do what we can…and if we do not know…we make an approximation…3-5x, 5-10 a month for the last 20 years, somewhere around 50 times, around 10x, or even if needed “many times”, “many many times” etc
(I should note that if one is “remarried” or “married” to a divorced person…or in an invalid marriage etc or “living together”…one needs to take care of that first…or speak to the Priest …not that these apply to you…but for readers)
Of course one needs contrition and a firm purpose of amendment. (remember though feelings need not occur…)
Here from the Catechism:
scborromeo.org/ccc/p2s2c2a4.htm#VII
Here is a guide sold by Catholic Answers:
shop.catholic.com/product.php?productid=137&cat=25&page=1
Remember Jesus loves you and wants to forgive you and to give you life. So that you may return to Holy Communion and receive him there (one needs to wait until confession…and if one does not know about the Eucharist …or forget…speak with the Priest etc for one will need to know more too first)
And do not be afraid…perhaps make an appointment to see the Priest outside normal confession time…and ask him to help you
Here is an overview of the Faith
vatican.va/archive/compendium_ccc/documents/archive_2005_compendium-ccc_en.html
(you can get it as a book…also get the Catechism at some point it is a treasure chest!)
Jesus is the
Good Shepherd …he loves you and desires to give you* true life*.
And do not forget the effects of the Sacrament (Catechism) :
IX. THE EFFECTS OF THIS SACRAMENT
1468 "The whole power of the sacrament of Penance consists in restoring us to God’s grace and joining us with him in an intimate friendship."73 Reconciliation with God is thus the purpose and effect of this sacrament. For those who receive the sacrament of Penance with contrite heart and religious disposition, reconciliation "is usually followed by peace and serenity of conscience with strong spiritual consolation."74 Indeed the sacrament of Reconciliation with God brings about a true “spiritual resurrection,” restoration of the dignity and blessings of the life of the children of God, of which the most precious is friendship with God.75
1469 This sacrament reconciles us with the Church. Sin damages or even breaks fraternal communion. The sacrament of Penance repairs or restores it. In this sense it does not simply heal the one restored to ecclesial communion, but has also a revitalizing effect on the life of the Church which suffered from the sin of one of her members.76 Re-established or strengthened in the communion of saints, the sinner is made stronger by the exchange of spiritual goods among all the living members of the Body of Christ, whether still on pilgrimage or already in the heavenly homeland:77
It must be recalled that . . . this reconciliation with God leads, as it were, to other reconciliations, which repair the other breaches caused by sin. The forgiven penitent is reconciled with himself in his inmost being, where he regains his innermost truth. He is reconciled with his brethren whom he has in some way offended and wounded. He is reconciled with the Church. He is reconciled with all creation.78
1470 In this sacrament, the sinner, placing himself before the merciful judgment of God, anticipates in a certain way the judgment to which he will be subjected at the end of his earthly life. For it is now, in this life, that we are offered the choice between life and death, and it is only by the road of conversion that we can enter the Kingdom, from which one is excluded by grave sin.79 In converting to Christ through penance and faith, the sinner passes from death to life and "does not come into judgment."80