First off, how do I do a confession? Last time I went I kinda walked in there and sate down, but I remember in second grade we said a little prayer out loud behind the curtain before we sat down in front of the priest. How am I supposed to do this?
If you need help, you can always ask the priest to guide you through your confession.
In general, though, once you enter the confessional the priest may greet you somehow.
After this, you make the sign of the cross.
Then you may tell the priest some relevant background information such as how long it has been since your last confession and your state in life (single, married, etc.).
Then tell the priest all your mortal sins by kind and number.
You may also include (and are encouraged to do so) any venial sins you have committed.
Once you are finished, it’s helpful to give the priest some clue that you’re done such as, “so for these sins and the sins of my past life I am truly sorry.”
The priest may give you some advice or ask questions, etc.
The priest will give you a penance, then he may ask you to make an act of contrition. There are several common Acts of Contrition, but the essential elements which it should include are: I am sorry for my sins and by the help of God’s grace I resolve not to sin any more.
Lastly, the priest will give you absolution and send you off.
Note that there may also be some variations such as a scripture reading at some point, etc.
Don’t worry too much about it, though. It may even be helpful to tell the priest that it’s been a long time since your last confession or that you don’t remember what to do exactly. Not a problem!
Also, I plan on confessing 2 mortal sins. I have received the Eucharist while in a state of mortal sin. Should I confess this as well? And is it okay to confess 2 mortal sins in one sitting?
Yes. You should confess the number of times (as best you can remember or approximately) that you received the Eucharist or other sacraments in a state of mortal sin.
Not only
may you confess two mortal sins in one sitting, you are always required to confess all your mortal sins (by kind and number) unless it is not possible to do so (e.g., you legitimately forget to mention it). Deliberately withholding a mortal sin will invalidate your confession such that you will be absolved from none of your sins and will have committed the additional grave sin of sacrilege.
Don’t be too worried, God loves you and wants you to be in good standing with him and the Church again. God bless!