I’m a bit confused on some things.
Unless you’d be uncomfortable doing this, I suggest you ask your questions to a priest at your new parish.
Who goes up for Communion?
Only Catholics who have fasted from food and drink (water and medicine excluded) for at least
one hour and who have confessed
any mortal sin they are aware of having committed.
Am I supposed to go to confession?
At least once a year. You should make it a habit (monthly is a good idea). If you have committed mortal sin (like “not been a practicing Catholic for several years”), you must go to confession before you start receiving Holy Communion again. Otherwise… you’re committing a mortal sin by doing so.
The priest mentioned Lent today, what is that all about?
Lent is the liturgical season that precedes Easter. It is a time of penance (primarily by fasting and abstinence) and spiritual self-inspection.
And what makes me a Catholic (being baptized Catholic)?
There is only one baptism and only one Church, and anyone who is baptized is baptized into that one Church, the Catholic Church. Whether they are baptized into a Catholic
parish is another matter altogether. A Catholic, technically speaking, is a Christian who believes the Catholic faith.
And when do I genoflect? I forgot to do it before going into the pew today. Do I do that everytime I enter the pew? Are there other times I should do it?
You normally genuflect to the tabernacle (when the Eucharist, the Blessed Sacrament, is inside it) and to the Eucharist in general. I genuflect before I enter my pew when I arrive, and after I leave my pew after Mass.
What things do I confess to if I’m supposed to confess at all?
You should confess in type and number any and all mortal (serious/grave) sins you can remember having committed since the last time you confessed. Confessing venial (minor) sins is praiseworthy although not strictly required.
When do I make the sign of the cross, when do I bow my head?
During the Mass, the sign of the cross is only made at the beginning of Mass (when the priest says “In the name of the Father, and of the Son, and of the Holy Spirit”) and end of Mass (when the priest says “and may Almighty God bless you, Father, Son, and Holy Spirit”). You would also do it when entering a church when you bless yourself with holy water.
Bowing your head… this is traditionally done when the Trinity is named (“Father, Son, Holy Spirit” – so your head should be bowed when you make the sign of the cross) and at the name of Jesus (at least when it is said in the Mass). At the name of Mary or the saint being commemorated that day, a smaller bow of the head is customary. You should bow your upper body during the part of the Creed (said at the middle of Mass) when you say “By the power of the Holy Spirit, he was born of the Virgin Mary and became man”.