There will be events preceding Christ's return to Earth. He will take His believers up into Heaven without coming down here Himself. The church calls this the Rapture, but that word isn't used in the Bible.
Straight after the Rapture, the Antichrist will be revealed. The seven year Tribulation then begins. The first half, 3.5 years, will be increasingly horrible. The second half, the Great Tribulation, will be dreadful. A large proportion of the population will be killed.
That will end with Christ's return. He will come in glory, as an adult. Everybody will know that He is Lord. People who have become believers between the Rapture and Second Coming and who have survived the Tribulation (many will have died) will join Jesus in His thousand year reign on Earth. Non believers will be sent to Hell.
It's important to know that the Bible says non believers cannot accept Jesus and His salvation once He returns. To be saved, people must accept Jesus before His return. To be taken to Heaven before the Tribulation, they must be saved before the Rapture.
Timing -
Second Coming is 7 years after the Rapture.
The Rapture could happen any time now. All Bible prophecies required to precede it have already been fulfilled. With the world in such turmoil and the increasing pace of political, military and societal change, it looks as if the Rapture will happen soon.
Disclaimer. Some Christians have different interpretations, but I believe this one is the majority view.
This link may help:
www.thelivinggospel.org/studies/end-times/the-second-coming
BTW this site offers a free ebook on the Rapture, and a special offer of two more ebooks for $0.99. I got the freebie, but the page didn't work for the $0.99 offer for me.