Every one who wants to be right with God must have faith (belief) in his Son Jesus Christ. This comes from hearing the word of God, the gospel which God revealed.
Why believe in Jesus?
Jesus is going to judge all mankind, including you and me. He will reward those who have followed him, and punish those who have rejected him (2Tm 4:1,8 2Th 1:8-12).
Where is the evidence to warrant belief?
There are four written testimonies that record the signs and wonders that Jesus did, including his coming back from the dead. These were written that we might believe that Jesus truly was the Son of God (Jhn 20:26-31).
God has made sure that everything necessary to belief has been revealed and recorded in the holy scriptures. "So then faith (or belief) comes by hearing, and hearing by the word of God" (Rom 10:11-17). This shows how belief, the first step to salvation, comes about. God provides the evidence in his word. By honestly and earnestly hearing that word we can believe. Faith comes from God, not from ourselves. We don't listen to our own hearts. That won't produce a true belief. We listen to God's word. That produces true belief unto salvation.
Isn't there anyone else we might just as well believe in?
No. Jesus is God's unique Son. He is the one whom God gave to the world.
There is no one else through whom we may come to God (Jhn 3:16, Jhn 14:6,
1Jn 5:10-13).
Is believing all that we need to do?
No. A belief without actions is a belief useless and dead (Jas 2:20-26). Believing in Jesus means doing what he says (Jhn 15:14, 1Jn 3:23-24)..
When we believe in Jesus what should we do?
Here is the answer given to those who asked that question:
"Repent (change your heart) and let each of you be immersed in the name of Jesus Christ, for the forgiveness of sins..." (Acts 2:37-38). That is how one begins to put belief into action.
Note that this is God's answer (God having spoken through Peter) to the question, "What must we do?" (Acts 2:37). I observe with fear and trembling, that many preachers are not giving that answer today, but a different answer.