This is one of the more famous passages of the bible - it is the essence of biblical christianity and therefore a good one to know. If comes from John’s gospel, chapter 3, verse 16.
The context of the verse is a conversation Jesus has with a Pharisee called Nicodemus. Nicodemus comes to Jesus to find out more about what Jesus is saying and in response Jesus talks about desperately helpless humanity is because of their sin - we have to be “reborn”, renewed, or born of the Spirit, if we are to have any hope of entering heaven. Nicodemus does not understand so Jesus puts it plainly - humanity cannot save themselves so God sent his Son so that through his death (being “lifted up”), whoever believes in him will be forgiven, reborn of the Spirit and enter heaven.
It is a fundamental passage that shows us what we need to do if we want to be forgiven by God and spend enternity with him.
If you have any questions abotu this then please get back to me.