What is “rising”? In death, the separation of the soul from the body, the human body decays and the soul goes to meet God, while awaiting its reunion with its glorified body. God, in his almighty power, will definitively grant incorruptible life to our bodies by reuniting them with our souls, through the power of Jesus’ Resurrection.
Who will rise? All the dead will rise, “those who have done good, to the resurrection of life, and those who have done evil, to the resurrection of judgment.”
How? Christ is raised with his own body: “See my hands and my feet, that it is I myself”; but he did not return to an earthly life. So, in him, “all of them will rise again with their own bodies which they now bear,” but Christ “will change our lowly body to be like his glorious body,” into a “spiritual body”:
But someone will ask, “How are the dead raised? With what kind of body do they come?” You foolish man! What you sow does not come to life unless it dies. and what you sow is not the body which is to be, but a bare kernel ….What is sown is perishable, what is raised is imperishable…. the dead will be raised imperishable…. For this perishable nature must put on the imperishable, and this mortal nature must put on immortality.
This “how” exceeds our imagination and understanding; it is accessible only to faith. Yet our participation in the Eucharist already gives us a foretaste of Christ’s transfiguration of our bodies:
Just as bread that comes from the earth, after God’s blessing has been invoked upon it, is no longer ordinary bread, but Eucharist, formed of two things, the one earthly and the other heavenly: so too our bodies, which partake of the Eucharist, are no longer corruptible, but possess the hope of resurrection.
When? Definitively “at the last day,” “at the end of the world.” Indeed, the resurrection of the dead is closely associated with Christ’s Parousia:
For the Lord himself will descend from heaven, with a cry of command, with the archangel’s call, and with the sound of the trumpet of God. and the dead in Christ will rise first.
From the Catechism of the Catholic Church 997-1001