What a question! These are big issues that Christians have wrestled with throughout the centuries. The idea of someone being both God and human is mind-blowing - and it’s very tough to get your head around.
Jesus is fully God
At the start of his gospel, John explains what it means for Jesus to be God (John 1:1-5). Firstly, he explains that it means Jesus is eternal. In other words, He was not created, but has always existed. Secondly, it means that Jesus is the creator of all things that have been created. There is nothing that exists that doesn’t have the label ‘made by Jesus’. All life finds its source in the person of Jesus. Paul writes the same things in Colossians 1:16-17.
Jesus is God on earth
John goes on to explain the staggering fact of the ‘incarnation’ (John 1:14-18): This God - the creator and sustainer of all things - chose to enter his creation. He became truly human and lived among us. In the (human) person of Jesus we see God fully.
Jesus is fully human
The picture the gospel writers give us of Jesus is one of someone that is distinctly human. He became flesh (John 1:14). He got hungry and was tempted like we are (Luke 4:1-13). Even after his death and resurrection, Jesus goes to great lengths to show he is still fully human; he shows his hands and feet, and eats with them, all to show that he is not a ghost (Luke 24:36-43). And he was raised as a human and is still human now, the first of many humans in heaven.
Jesus can help because he is both God and human
The fact that Jesus is both God and man is very important for us. As a human who shares in our human weaknesses, he knows what it is like to be human and tempted and is therefore able to represent us in the presence of the Father where he pleads to Him for us (Hebrews 5 and 7). Because he is fully God, he is able to show us what God is like (John 14:8-11) bu more important because he is God, he is able to pay for our sins and bring us into a relationship with God again (Colossians 1:19-20). In other words, the problem that we find ourselves in, the alienation that our sin brings between us and God, Jesus can fix because he is both man and God, he is able to reconcile us.
I hope this has helped you in your thinking about Jesus…. Feel free to ask some follow up questions!