A fair question.
The big problem here is that christianity is divided into so many branches, so many churches, so many opinions of this or that...
One might be confused. And I am confused.
The christian society is so diversified that it's impossible to come with at straight answer to these things. Better than asking "Do you believe in God" is asking "What sort of God do you believe in".
Your confusion is understandable. The freedom of religion in the USA in the 1600s caused the proliferation of denominations that confused Joseph Smith, so he asked God which one was true and perceived God's answer was "None of them, so start a worse one." Well, the second part of that answer is mine. What I believe is God's answer and the key to becoming less confused is to distinguish between what beliefs are essential and which are secondary and more debatable. When one does this he finds that all Christian denominations agree on what I call the kerygma, which I summarize as follows:
A crisis that threatened a Philippian jailer with death prompted him to ask Paul and Silas
the most important question in life: “What must I do to be saved?” (Acts 16:30) This question, "What is God's requirement for salvation?" (GRFS) is most important, because—as sinful and mortal souls—we need saving from corruption, both moral and physical. We need saving from physical death if we value or enjoy life, and we need saving from immorality or evil-doing if it results in unhappy existence, especially after this lifetime.
Jesus expressed GRFS succinctly by saying “Repent” (Matt. 4:17) and “Ask… seek… knock…” (Matt. 7:7, Heb. 11:6, Isa. 45:19), implying that God gives every sinful soul the ability to repent and seek salvation (cf. 1Tim. 2:3-4, 2Tim. 2:25, Ezek. 33:11), which might be why Paul said sinners are saved “by grace through faith” (Eph. 2:8-9, Tit. 2:11). Seeking God is the beginning of saving faith, and not repenting or rejecting God’s salvation in Christ is the essence of evil atheism or faith in I-dolatry (Rom. 3:11, 1:18-23).
The reply of Paul and Silas to the jailer was, “Believe in the Lord Jesus.” (Acts 16:31). This is GRFS in a nutshell:
“Accept Christ Jesus as Lord” (as also in 2Cor. 4:5 & Col. 2:6). The main points of Christian orthodoxy implicit in this statement can be explained or elaborated as follows:
- There is a/one all-loving and just Lord or Creator God (Deut. 6:4, John 3:16, 2Thes. 1:6), who loves sinful humanity (Rom. 5:6-8, John 3:16) and who is both able (2Tim. 1:12) and willing (1Tim. 2:3-4, Ezek. 33:11) to provide all morally accountable human beings salvation or heaven—a wonderful life full of love, joy and peace forever.
- Human beings are selfish or sinful (Rom. 3:23, 2Tim. 3:2-4, Col. 3:5), miserable (Gal. 5:19-21), and hopeless (Eph. 2:12) or hell-bound at the judgment (Matt. 23:33 & 25:46) when they reject God’s salvation (John 3:18, Rom. 2:5-11).
- Jesus is God’s Messiah/Christ and incarnate Son, the way that God has chosen (John 3:16, Acts 16:30-31, Phil. 2:9-11) of providing salvation by means of his atoning death on the cross for the payment of the penalty for the sins of humanity (Rom. 3:22-25 & 5:9-11), followed by his resurrection to reign in heaven (1Cor. 15:14-28).
- Thus, every person who hears the NT Gospel needs to repent and accept God’s grace or justification in Jesus as Christ/Messiah the Lord or Supreme Commander (Luke 2:11, John 14:6, Acts 16:31), at which moment God’s loving Holy Spirit of Christ indwells/baptizes the believer into the church (Rev. 3:20, Rom. 5:5, 1Cor. 12:13).
- Loving Christ Jesus as Lord (Luke 2:11), God the Son (Matt. 16:16) or God in the human dimension (Col. 2:9) means reflecting divine love (DL) as empowered by the Holy Spirit, thereby obeying His command to love one another (Matt. 7:21, 22:37-40, John 13:35, Rom. 13:9)—forever (Matt. 10:22, Psa. 113:2), which will eventually achieve spiritual maturity on earth and heaven after Christ returns at God’s resurrection (John 14:6, 17&26, Rom. 8:6-17, Gal. 6:7-9, Eph. 1:13-14, Phil. 3:12-16, Heb. 10:36, 12:1, Jam. 1:2-4).
GRFS may be denoted by the use of the Greek word kerygma, meaning proclamation or preaching, referring to the good news (Gospel) concerning salvation to heaven and from a just hell (the DOD, cf. Rom. 1:16, Gal. 1:6-12, Col. 1:21-23). This Gospel was preached by Peter (in Acts 2:22-24) and summarized by Paul (in 1Cor. 15:1-8). The salient points include: Jesus was a man (1Tim. 1:16), accredited by his sinless life (Heb. 4:15) and ministry (John 10:37-38) to be God’s Messiah, who died on a cross as the sacrifice for humanity’s sins (Rom. 3:25), but who was resurrected from the dead to show his divinity (1Cor. 15:20, Rom. 1:1-4). Messiah is the Way to heaven (John 14:6).
An obvious question to ask at this point is,
“What is GRFS for those who have never heard of Jesus?” (which includes everyone living B.C. and millions of people who have lived A.D.) If God loves the world (John 3:16) and wants everyone to be saved (2Tim. 2:3-4, Ezek. 33:11), then He must provide an opportunity. God’s just judgment is illustrated by Jesus in the Parable of the Talents (Matt. 25:14-29), which indicates that God will judge souls on the basis of the truth (Word = Christ per John 1:1f.) they have received.