So, a really long time ago, there was a man named Jesus who people believed was a special person sent from God. He traveled around teaching people about love and kindness and doing miracles like healing sick people and feeding lots of people with just a little bit of food.
One day, Jesus and his friends were traveling to Jerusalem for a big celebration called Passover. Lots of people heard that Jesus was coming and they got really excited because they wanted to see him and hear what he had to say.
When Jesus got near Jerusalem, he told his friends to go get a donkey for him to ride on. This might seem strange, but it was actually an important symbol of a king coming to visit. The people who saw Jesus riding on the donkey saw this as a sign that he was a special king sent from God.
So, when Jesus came into Jerusalem riding on the donkey, lots of people lined the streets and waved palm branches and shouted, "Hosanna!" which means "save us now!" They believed that Jesus could save them from their problems and they were very excited to see him.
This special entrance that Jesus made into Jerusalem is called the "triumphal entry" because it was like a big celebration of his arrival. It's an important event in the Bible because it shows how much people believed in Jesus and how much they hoped he could help them.