I assume you were Baptized at the Easter Vigil!
When you make your first confession…well you tell the priest it is your first confession…tell your state of life (which would be single assuming your going sooner than years)…and you accuse yourself of your sins…etc
All Mortal sins in number and kind (and circumstance that changes the sin…like it was your brother you murdered) must be confessed.
(one can not hide even one…such would make the problem bigger! and be invalid…and you would have to confess that fact along with all the mortal sins that you tried to confess and the one you hid! So do not do that. Forgetfulness is a another story…that can happen. But one is to confess it in the next confession once one remembers it)
Murder 3x etc
(but lets avoid mortal sin )
Venial sins need not be confessed…they can be forgiven in many ways…but it is recommended to confess at least some…
They can be confessed in various ways…and no need for the number.
There are little guides for the “format” of confession online …
It is very good to go to confession regularly.
One could go every other week…or every week…or once a month.