In regards to #2, are you referring to confessions of sins to Jesus Christ of confessions of sin to the priest?
Yes. It’s the same confession. During Confession, the priest acts
in persona Christi like he does when consecrating the Host every Mass. It’s still God forgiving the sins or consecrating the Host. It’s just that he acts through the priest to do so. To relate it to the events of the Bible, it’s a similar concept to the miracles the apostles worked in Acts. Paul didn’t have the power to raise Tabitha from the dead. Instead, God worked through Paul to do so.
So now onto the actual question, of how Catholics define and view salvation.
First off, salvation. Believe it or not, Catholics agree that you can’t lose your salvation. The difference, though, between you and I saying that, is that Catholics don’t say a person is saved until they’re through the pearly gates. (Okay, technically in Purgatory, but that’s a different debate)
Instead, what you would call salvation is probably closer to what Catholics would call justification. When a person is baptized, they’re justified, meaning they’re cleansed of any sin (original or actual) and begin receiving God’s saving grace. Of course, however, they’re still a sinner. We’re still in this fallen world we like to call Earth. So our random John Doe messes up and sins. Now if it’s a venial sin, he’s still in the clear. But if it’s a mortal sin, then he just cut himself off from God’s grace. But, of course, God is infinitely forgiving, so he can confess his sins and begin receiving that grace again. This is called being in a state of grace.
I, of course, reference 1 John. In 1 John 5:16-17, there’s mention of sin which leads to death, and sin which does not lead to death. Mortal sin is the former. (And indeed, the RSV even translates it that way) It cuts us off from God’s grace. Venial sin is the latter. It doesn’t cut us off, but it’s still sin. It can still lead us to mortal sin. Think of venial sin as the gateway drug of the sin world. Is it bad? Yeah. Is it entirely deadly? Not really. Is it still going to lead you to do the more hardcore stuff like mortal sin? Yeah.
So finally, what happens when our John Doe dies? If he’s in a state of grace, he goes to Heaven (with a side trip through Purgatory). If he’s not… Well the Catholic Church will never actually say someone’s going to Hell. There’s always the chance that God saves more people than just those in a state of grace. Such as the invincibly ignorant, those who never heard of Jesus.
And finally, Purgatory. I begin with two questions for you. On earth, is humanity in a sinful, fallen state? Yeah. Now when we get to Heaven, are we in a sinless, perfected state? Yeah. Well wait, what happened? We went from being sinful to being sinless. I am positive you agree some sort of event happens after we die to cleanse us completely of sin, and make us perfect enough to be in Heaven. That’s what Catholics are saying with belief in Purgatory. We’re merely giving that final cleansing, or
purgation, a name.