The word "Gospel" is a word that comes from the Old English "god-spel" which means "good news".
The Gospel is indeed good news, but first we need to hear the bad news. The bad news is that God is holy, and not just holy, but infinitely holy and good.
This is bad news because we are not.
Sin, which is all those bad things we do in our rebellion against God that God doesn't like, separates us from Him. And since God is infinitely holy, our sin causes us to be infinitely separated from Him too, something the Bible calls "spiritual death", or simply "death".
We know that nobody is perfect, and the Bible tells us that all have sinned, which means that we are all infinitely separated from our Holy God and Creator as a result of our sin. Physically dying in that state causes that state of separation to be permanent, something most people refer to as "going to hell". It is important to understand that once you enter this state, it is eternal, there is absolutely no getting out of it.
If we are spiritually dead, the question that inevitably arises is "What can a dead person do?" How can we, being dead, remedy our situation? Unfortunately, there is absolutely nothing you can do to "make up" for your sin. Our sin is an infinite offense against God because God is infinitely holy, and since we ourselves are finite beings, we cannot make that infinite payment of justice we owe God. This is why the state is eternal if it is not remedied in life. No amount of good works, charity, kindness to others, or anything else will ever be enough to make up for your sin and earn your justification before God. Much like how no amount of charity, or good works would ever be enough to cause a judge to forgive a murderer. That would not be justice, and since God is also perfectly just, He cannot simply forgive people who have broken His holy law. How would you feel if that murderer had murdered your family, and the judge just let him free? What if the murderer promised to "never do it again"? Would you think it fair and just if he was forgiven by the judge then? So you see, just doing good things, and promising to never do bad things again is simply not enough to be forgiven. Justice must be served.
And this is where the good news comes in. The good news is that Jesus Christ, the unique Son of God, who was born of a virgin and lived a perfect life on Earth, fulfilling the law of God perfectly, and never sinning, died on the cross to pay the penalty of sin for those who place their trust in Him. On the cross, Jesus paid the full penalty for the sin of His people, receiving the full punishment that we sinners deserve. He then died and resurrected on the third day to proclaim His victory over sin and death. For those who fully place their trust in Christ, and not in their own works, deeds or anything else, all sins are paid for in full and their standing before God is made completely right. And not just that, because salvation is entirely His work, He also promises that nobody can snatch us out of His hand, because "He who started a good work in you, will see to its perfection". God offers salvation in no other way, the only way to the Father is through Jesus Christ, and there is salvation in no other name. No institution, church, religion, denomination, pastor, priest, preacher, religious leader, or anything or anyone else can offer salvation. There is salvation only in Christ.
When God saves a sinner, He grants them the gift of faith, which is that full trust in the redeeming work of Christ on the cross. He grants repentance, which is the turning away from sin and turning to God, so that sin you once loved you will now hate, and it will be replaced by a burning desire to seek holiness, righteous living, for the glory of your God and Savior alone. You will have a deep hunger for His Word, to know Him and His will for you better. All these supernatural changes to your heart will produce the fruit of repentance: holy living. Not perfect living, but a continuous conforming to the image of Christ, a daily growth in maturity and holiness, a process called "sanctification". And as Jesus said "unless you repent, you will all likewise perish". God does not grant salvation without repentance. And repentance necessarily produces holiness.
God calls all men to repent. Therefore, obey His command and repent. Believe that Jesus, the unique Son of God, and second person of the Trinity (one God, 3 persons) died for your sins and rose on the third day. Trust only in Christ for your salvation, and not your religion, your works, or your ancestry (your parents, your culture, your lineage). There is salvation in no other. Repent and believe, and trust only in Him, and be saved!
God then calls us to test ourselves, to make sure that indeed we have been saved. Check your attitude toward sin, toward your own sin. If you are not repulsed by it, and fighting it as though your very soul depends on it, then seek the Lord and repent, eternity is not something you want to gamble with. Repent and believe... today is the day of salvation.