Who told you all this? - because it can easily be disproved from scripture.
If you look at Matthew 24, the famous 'Olivet discourse' in which the Lord Jesus talks about the destruction of the Temple, the end of the age and his second coming (24:3), you will see the context in which he spoke about 'this generation' (24:34). In context, 'this generation' is the generation that will see 'all these things' (vs.33).
What things? - well, especially the flourishing of 'the fig tree' (= Israel) and also all the other 'signs of the times' - eg. false prophets, deception, tribulation of the saints, wars, famines, pestilences and earthquakes. It is the generation that sees all these things which will also see the Lord's return in glory.
Also, in Matthew 24, there is a description of what the Second Coming will look like : 'as the lightning comes from the east and flashes to the west' (vs.27) and also 'they will see the Son of Man coming on the clouds of heaven with power and great glory' (vs.30).
Now, ask yourself, did that happen at Christ's resurrection? Did 'every eye' see him (Rev.1:7)? At his resurrection, did he come in the clouds, or did he rise from the ground? And, if it is according to your version, then why did the angel stand by the apostles, as Christ was ascending into heaven, and inform them that 'this same Jesus, who was taken up from you into heaven, will so come in like manner as you have seen him go into heaven' (Acts1:11)? If the Second Coming had already happened, then did the angel get it wrong?
For, according to the angel - and also the doctrine of Paul and the other apostles - the Lord Jesus, having returned to his Father in heaven, would sit on his throne until the time came to come again, back to the earth.
Here you have it: after the ascension, here is Peter saying that Christ is yet to come again to the earth:
Ac 3:20-21 And that he may send Jesus Christ, who was preached to you before, whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
Yes, the Lord will come again in 'the times of restitution (= restoration) of all things and, until that time that the Father send him, he must remain in heaven.
You are confused, and you need to read and study your Bible more, because there are lots of references to the Lord's Second Coming, just all over the place. Like, for instance, the Olivet Discourse (Matt.24) is also in Mark 13 and Luke 17 and 21. Also, it's dotted about in most of the Epistles, especially I and II Thess.
The 'beginnings of sorrows' (Matt.24:8 and of 'great tribulation' (24:21) describe a period yet to come in world history, which is called in the Old Testament 'the Day of the Lord' - of which (according to Acts 3:21) there was much prophesied through Israel's 'holy prophets' before the Lord first came.
This is a very big subject, so much so that 2/3rds of all prophecy is devoted to it - what will happen in 'the Day of the Lord'. It clearly is yet future, so don't jump to any hasty and ill-thought-out conclusions that scripture will not back up.
There are no 'quick fixes' on this one, and a lot of hot debate! Just read the scriptures, read the commentaries, ask, learn, pray and ponder and you'll end up a lot wiser. And, if you really want to know the truth, you'll get there in the end.