One difference between the Catholics and Episcopalians is that the Episcopalian church ordains women to the priesthood while the Catholic church does not as of 2015. Another difference is that clergy are allowed to marry in the Episcopalian church, a practice forbidden to Catholic priests. A less obvious difference between the two churches is that each of the Episcopalian churches governs itself with a national leader as opposed to being under the control of one worldwide leader, as with Catholics.
The Episcopalian church is the American branch of the British Anglican church. The Episcopalian church was founded during the American Revolution and is part of the Worldwide Anglican Communion. It is important to note that each Episcopal church is governed nationally or regionally. While the Archbishop of Canterbury is the spiritual head of the church, he is not able to dictate how the American churches are governed. This is very different from Catholicism, for which the Pope is both the spiritual head and the final authority for all Catholics worldwide.
Recently, the Episcopalian church has shown support for and conducted same-sex marriages. This is not allowed or even under consideration within the Catholic church. Divorce and remarriage are allowed in the Episcopalian church but not in the Catholic church.