In the beginning God created everything.
He created mankind and built a beautiful Garden for them to live in. It was part of His Kingdom so it was perfect and there was nothing in it to defile it. In this Garden there was no death and decay. All was perfect. God was King of this garden.
In this garden God and man had a close personal relationship, walking and talking together as close friends would. Man had everything He needed except a wife. So God gave man a woman to be with the man forever as his wife and partner. She too enjoyed this close, personal relationship with God.
However, they both disobeyed God and by this rebelled against him (They rejected His rule over them). God was King of this beautiful, perfect place they were in. They had rebelled against their ruler. This is called treason which is punishable by death or banishment from the kingdom of the King.
The man and the woman suffered both fates. They were cast out of the garden into the only other place available for them which was the enemy's kingdom on earth. and would now die physically. The earth was a place of imperfection God had prepared for His enemy: Satan, the devil. The world they were in started to decay and no longer was perfect. They were now in a place ruled by the enemy of God.
The man and the woman both died, spiritually, because they could no longer go and talk to God and would be forever separated from Him after their death in the place His enemy ruled.
Whoever king you serve when you die is the one whose kingdom you go to when you die. If God is your King you are restored to the relationship that the man and the woman lost through their rebellion.
If you do not go to be with God in His Kingdom you go to the only other place left, which is called hell, where Satan is king and he hates people so that he really causes them to suffer terribly. God does not send people to hell. They go their because they have chosen to follow Satan and rejected what Jesus required of them. This is because they have done something which they know is wrong and refuse to give it up. Because they are defiled by sin they cannot enter heaven where all is undefiled. Or by default, ignored Jesus so it was the only place left for them to go too.
So man was in this predicament. God required a punishment for their rebellion and mankind was not able to meet it as God is infinite and man is finite. The rebellion required an infinite punishment for restitution to God and mankind is finite so could not meet this requirement.
God saw that He alone could do something about this situation. God is Love by nature so He sent Jesus to die on Calvary and meet God's requirements of mankind's punishment for every one that ever lived if they decided to wholeheartedly try follow Jesus as their King.
So Jesus met the requirements of God's punishment and mankind was once again able to have God as a close, personal, friend and to go to the beautiful place called heaven when they die where the original perfection of the garden exists, where these is no death or decay and all is perfect.
What must you do to get to heaven?
You must believe Jesus is Lord of all, that He is God, who came to and died for you on Calvary, redeemed you (removing every barrier between you and God) so that you can now enter heaven and then you must try wholeheartedly to obey Him in all He asks you to do which means:
You need to study His guidebook, The Bible and find someone who can teach you what it means to be a Christian and not just preach to you once a week in church and that you also need to find a group of Christians you can socialise with and be encouraged by them to live as a Christian.
You also need to be guided by The Holy Spirit so you know what God desires you to do for Him.
You also need to find a church that believes The Bible which will help you in the Christian life God has given you.
You also need to learn how to be guided by The Holy Spirit so He can tell you what God would like you to do.