God is a perfect being. He's holy, loving, and just. He made us to worship Him and love each other. We didn't.
"For all have sinned and fall short of the glory of God." (Romans 3:23)
Our sins are many. Everyone who does evil will face God's judgement. His enemies go to Hell: a lake of fire where they never get rest and the smoke of their torment goes up forever and ever. But, there's good news:
"But God gives proof of his own love toward us, in that while we were yet sinners, Christ died for us." (Romans 5:8)
"For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord" (Romans 6:23)
"For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures" (1 Corinthians 15:3-4)
"[Jesus said:] This is the will of the one who sent me, that everyone who sees the Son, and believes in him, should have eternal life; and I will raise him up at the last day." (John 6:40)
"Therefore, repent and be converted, that your sins may be blotted out." (Acts 3:19)
Jesus was God in human flesh. He lived the perfect life we didn't, died for our sins, and was raised again. If you commit your life to Him (believe), He saves you by what He did for you, not your own works. To return to God, just say this to Him (i.e. pray) right where you are:
"Dear God, I know that I am an unworthy sinner and there is nothing that I can do to earn your salvation. I believe Jesus is man and God. I believe you sent Him to live the life I didn't, that He died on the cross for my sins, and was raised from the dead three days later. I repent (or turn away from sin) and accept Jesus Christ as my Lord and Savior. God I ask in Jesus' name that you please forgive and save me. Thank you. Amen (the end)."
If you meant it, then you now have peace with God. The Spirit of God now dwells in you. The washing of regeneration and the renewal of the Holy Spirit will change you into a new person from the inside out. Now, seek the things that are above, where Christ is, seated on the right hand of God.
You pray that, start living as a believer, and be baptized to publicly demonstrate your faith. The evidence you did this is that the Holy Spirit will change your heart, or begin "sanctifying" you, to make you want to be more like Jesus. A need to love God and others more will begin to overflow out of your heart. You will need to spend time with God daily, studying His Word and praying, to grow as a believer. Join a local church that focuses on these things to help you do that. You will probably also face suffering in a world that hates God and righteousness. Endure it to the end since He is worth it.
God's Word is our ultimate authority for all matters on life. Get you a study Bible to understand it better. I recommend the English Standard Version (ESV). Read the New Testament first, starting in John. On the go, you can use a pocket Bible, online Bible, or Bible app.
My other site teaches the fundamentals. It also has a Quick Start guide to get you started. Read the whole thing. Dig into what links you find interesting. Get into a Biblical church to grow with others. Above all, be grateful because Christ has already secured your future by His own blood. It's a gift we did nothing to earn.