Previously, each Episcopal diocese made their own rules about whether same-sex couples could marry in that diocese's churches. For awhile there weren't very many that allowed it. It's gradually changed and Wednesday the entire Episcopal church approved the inclusion of same-sex marriage ceremonies. The change goes into effect in November.
The church also approved two new liturgies, one for same-sex and one for opposite-sex marriages. They also removed language indicating that marriage is between one man and one woman.
This is huge progress for the church which is considered by many to the closest to Catholicism.
Keep in mind that the rules which may apply regarding all couples marrying would still apply here - for example, couples would likely need to be members of the church, participate in pre-marital counseling and more.
This is incredible news in a week of amazing news...the world is changing in some great ways, folks!