Hi anon,
>How should I prepare for that?
When I first became Catholic and went for my first confession prior to baptism and confirmation I found making a list was a good way to start.
I found a good way for me to do it was to go through the seven primary sins and list everything I could under these.
Some such as gossip can be a bit harder to categorize but while you're listing all the sins you've done you'll come up with a lot.
When you're done with that you could try using: http://www.beginningcatholic.com/catholic-examination-of-conscience?fbclid=IwAR1lWgLq3YLGpx26k_88uwqRUypm26wQq-VzDP1FHbKkoJ8Zif3fk9mv9pk for a more in depth examination of conscience.
>Should I write every single sins I can remember in the span of all my teenager-adult in a sheet ?
>Should I write them "actively" with an examination of consciousness?
Yes to both. Make a list of all the sins that you can think of for yourself.
>Do I have to recall every single sins I did for all my life and confess them or I will go to hell if I can't recall them all ?
No. As long as you're not actively holding back any sins during confession, all will be forgiven in absolution. Typically I end my confession with "I'm sure there are many other sins that I have committed but do not come to mind at the moment."
Some suggest if they come back to you after confession you can confess them at your next confession, I'm not sure on the purpose of that aside from potentially getting advice from your priest. Seeing how you've been absolved.
Finally some general tips from someone who only converted some 3 years ago, so its still fairly fresh in memory.
>Tell your Priest that this is your first confession in over a decade and since you were a kid and not quite as knowledgeable in the faith.
He will likely tell you not to worry, maybe explain some things and help out if you're confused about something.
>At the end of confession you will be asked to make an act of contrition
This is essentially a prayer asking for forgiveness, confirming your resolve not to sin again. Typically a lot of Churches have these printed out on a bit of paper you can just recite. You can also just google act of contrition prayer. I typically just pray on the spot as an act of contrition.
>You will then be absolved of your sins and given your penance.
Carry out your penance the first opportunity you get, preferably right there in the Church. Typically you will be issued some prayers, or simply time to meditate with God and His mercy. I typically pray in the pews before the tabernacle.
Good on you anon, the sacrament of reconciliation is a wonderful thing. You will feel wonderful and renewed with the joy of God after. Let us know how it goes.
>One last thing, before confession with your list maybe before you leave to Church. I recommend praying to the Lord for forgiveness prior to confession, just go over your sins, confess your sorrow for sinning against the Lord and go through the list.
>Don't bring your list to the Church, try have a good understanding of all the things you want to confess. And don't sweat it if you don't list everything off. Even when I only have a few sins I sometimes forget a couple.
>That's why you're praying to God first, so you can list them all off to Him and ask forgiveness for it all.
>It's considered bad etiquette to take the list to confession, as typically a confession is better when it comes from the heart so to speak.
>I'm sure the priest wouldn't mind if you did though if it makes you less nervous.
God bless you anon, hope that helps.