A shepherd at the time of Jesus had two roles. The first was to protect the flock from thieves and wild animals, if necessary by putting his own life at risk. The second was to take the flock to pasture so the sheep could eat and drink and live.
So Jesus describes himself as the good shepherd. The 'flock' are God's people. Jesus risks and give his life for them so they will be completely safe. He gives us everything we need for eternal life, having laid his life down and taken it up again.
When Jesus said these things he got two reactions. Some found it strange and difficult and rejected him. Others found it equally strange but they felt that someone who did the things Jesus was doing had to come from God.
People told Jesus it was time to start speaking clearly. Jesus said he already had, and if they looked at things he was doing they would see that he came from the Father.
So it's simple and it's complicated. Jesus died. He rose again. He is God's Son. Anyone can accept this and receive what Jesus has to offer. And it's so wonderfully complicated it takes image after image to explain: the bread of life, the light of the world, the good shepherd etc etc.
More wonderful than we can ever imagine.