Okay, so imagine a really big group of people who love God and Jesus and want to worship Him in a special way. That's the Greek Orthodox Church!
They believe in the Holy Trinity, which means God is Father, Son (Jesus), and Holy Spirit all at the same time. They also believe in lots of saints who were really good people and did cool things, and they ask those saints to pray for them.
The Greek Orthodox Church has a lot of traditions that have been around for a really, really long time. They like to sing and chant during their church services, and they use special incense to make the air smell good.
They also have some rules about how to behave during church. For example, they stand up a lot and they don't sit in chairs. They also fast from certain foods during certain times of the year to show that they're thinking about God more than their own wants and needs.
Overall, the Greek Orthodox Church is a big group of people who believe in God and Jesus and want to worship them in a special traditional way.