John sees a beast coming out of the sea with ten horns and seven heads, with ten crowns on his horns, and on each head a blasphemous name. The beast resembled a leopard but had feet like those of a bear and a mouth like that of a lion. The dragon gave the beast his power and his throne and great authority. One of the heads of the beast seemed to have had a fatal wound, but the fatal wound had been healed. The world is astonished and follows the beast. Men worshiped the dragon because he had given authority to the beast, and they also worshiped the beast and asked, "Who is like the beast? Who can make war against him?"
The beast was given a mouth to utter proud words and blasphemies and to exercise his authority for forty-two months (3 1/2 years). This beast opens his mouth to blaspheme God, and to slander his name and his dwelling place and those who live in heaven. This beast has been given power to make war against the saints and to conquer them. He's given authority over every tribe, people, language, and nation. All inhabitants of the earth will worship the beast-all whose names have not been written in the book of life belonging to the Lamb that was slain from the creation of the world. He who has an ear let him hear. If anyone is to go into captivity, into captivity he will go. If anyone is to be killed with the sword, with the sword he will be killed. This calls for patient endurance and faithfulness on the part of the saints.
This first beast is the Antichrist. We can already see he's trying to copy Jesus Christ. In Revelation 6, we see him riding out on a white horse with a crown on his head. Jesus will show up in Revelation 19 riding a white horse, but He'll have many crowns. The Antichrist will be wounded to death but will be resurrected. It is believed that he will be shot in the head and will come back alive in 3 days. Jesus was crucified and God raised Him from the dead on the third day. Satan is forever trying to be like God so it's not surprising he'll try to copy Him. An even greater description of the Antichrist is found in Daniel 7:7-8, 24-25. Either way, many people are going to die during his reign. He'll come on the scene after the Rapture, but he'll be in real power the last years of the Tribulation since Satan himself will be living in him.
We then see a beast coming out of the earth. He had two horns like a lamb, but he spoke like a dragon. He exercised all authority on behalf of the first beast; showing miraculous sings and wonders causing people to worship the first beast. He could even call down fire from heaven to deceive the people. He ordered people to set up an image of the Antichrist in his honor. This image could talk and cause people to be killed who didn't worship it. This False Prophet also made all people small and great get the mark of the beast in their foreheads or right hands. Without this mark, a person can't buy or sell. In addition, anybody who doesn't take the mark will be beheaded. The mark is 666.
As we can see, we have been introduced to the satanic trinity, Satan, the Antichrist, and the False Prophet. Remember, Satan has been trying to be like God ever since rebellion entered his heart so it's not a surprise that he'll create something so abominable. In addition, we also see a familiar story with the False Prophet. In Daniel 3:1-7, King Nebuchadnezzar ordered an image in his likeness to be built and worshiped as well. Anybody who didn't worship the image was executed. Remember the story of the three Hebrew boys in the furnace? It's basically a past meets present meets future. The Old Testament and New Testament are greatly connected to each other, and both are relevant even today. Except for the yearly sacrifice because Jesus died once as a sacrifice and therefore, we don't need to kill any animals for the atonement of sins.
As for the mark, we do know it will be a 666. What we don't know is what it will look like. It's unknown as to whether it will be an actual number, barcode, microchip, or some sort of implant. But what is known is that this mark will tell the world and God that it is a sign that the person belongs to the Antichrist. That he/she has sworn their loyalty to the Antichrist and his system. Something to understand is that during this time, the world is such chaos, and everybody is going to be struggling to survive. Taking this mark will ensure that people can work so they can provide for themselves and their families. Have a place to live, and potentially have protection from getting executed. But is it worth it to take this mark? Why would the Antichrist kill those who don't take his mark? What's the catch?