Belief comes first. Hebrews 11.6 says,

"And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him."

We can't put our faith and trust in God and Jesus until we believe He exists, understand His message, and make a commitment. Only then can we live a life of faith based on that belief.

Therefore, faith and believe which one comes first?

When the Bible speaks to us about believing in Jesus, it means that we accept the truth that He is God, we believe what the Bible says about Him, we believe that what He teaches is true, and we align our lives with Him. So belief in Jesus is a full immersion into who He is and what He says, and we bring our lives into conformity with those truths.

Is that what you were asking? If not, try again. Or if some things I have said create more questions, please feel free to ask.

How do we concretely define believe?