The Tribulation period as specified in the Book of Revelation is a period of seven years in which the Earth will undergo various torments, plagues, and upheavals until the return of Christ.
As regards the Christian faith the trope applies as follows. Those who believer in Christ gain an immunity to most of the divine plagues and torments after being granted a seal that marks them as believers in Christ, which allows them to distinguish them from non believers which only they can see. A counterpart seal, referred to as the "Mark of the Beast", is granted those who oppose Christ and who support the Beast (the Big Bad more or less), but all this does is ensure they will be priority targets of the remaining plagues and torments.
While the exact scope of whatever supernatural powers will be granted is vague in some respects, the believers in Christ, on top of gaining divine protection from various divine events, they also will be given limited protection from all forms of harm at certain points. As for the enemies of Christ, some will be given the ability to call down fire to destroy their enemies by the Beast, the False Prophet who serves to make the Beast seem important and unstoppable, and by the Dragon who supports and later completely takes over the Beast (The Man Behind the Man of the Big Bad). They will also gain certain abilities to deceive the undecided to sway them away from Christ during this period.
At the end of this period (the Tribulation covers all seven years, the Great Tribulation starts at the halfway point and when it It Got Worse kicks in for both sides despite already being pretty bad after the first three and half years), when Christ returns, all who remained believers get to live a new world that is no longer a Crapsack World. As for the followers of the Beast, they, the False Prophet, and the Beast all get a Fate Worse Than Death.
I hope this helps.
