Within each member church of the Anglican Communion, there is what is called a Primate that leads that church. For most of these churches, the Primate is a Bishop, such as the Archbishop of Canterbury in the Church of England.
It might be tempting to think that the Presiding Bishop of The Episcopal Church is our Primate. That would actually be incorrect. The Presiding Bishop does just as the name implies: presides, specifically over the House of Bishops which is only one house of General Convention.
The actual Primate for The Episcopal Church is General Convention. This is the chief governing body that makes decisions that impact the entire church.
Since General Convention only meets every 3 years and the House of Delegates is a body elected from members of each Diocese, we need someone to represent us in the meantime. The Presiding Bishop often fills that role.
Others in the Anglican Communion often don't realize that the Presiding Bishop doesn't have the same authority as a Primate in other member churches. Presiding Bishops can't wave their hands to make a change. They have to work with the rest of their fellow bishops in the House of Bishops, and the Bishops themselves have to work with the House of Delegates.
Seeing this difference though can help us understand how The Episcopal Church operates compared to other churches in the Anglican Communion. It can also help us understand how others in the world look at us and interact with us too.