The primary difference between Catholics and Episcopalians is that Catholics believe in transubstantiation, the belief in the pope's authority and the need for private communion as well as different rules for priests, birth control and saints. Transubstantiation is the belief that the communion actually becomes the real body and blood of Christ when the priest prays over the communion.
Catholics believe in transubstantiation while Episcopalians do not. Therefore, Catholics believe that when they receive communion, they are actually receiving the body and blood of Christ into their own bodies.
Catholics believe that communion is an important act, and they will only allow Catholics who believe in transubstantiation to accept the Eucharist while Episcopalians will allow any one to receive the communion regardless of their profession of faith. Catholic priests must be men and cannot be married or have children. Episcopalian priests can be men or women and are allowed to be married and to have children. Catholics also believe in the pope's authority whereas the Episcopalians do not.
Catholics also do not believe in birth control while Episcopalians believe that using birth control is fine. Catholics believe that saints exist as a blueprint of the life that they should lead, but also that they should communicate and pray through the saints to ask for their guidance. Episcopalians do not believe in asking the saints for guidance and only use them as blueprint for their own lives.
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.