You may want to enlist the aid of Google to get at this in depth, but in brief:
Catholics teach that the bread and wine become, upon consecration, the body and blood of Jesus Christ, with only the appearances of the bread and wine remaining. The technical term for this is “transubstantiation,” and the teaching precedes the term by many centuries. The Eastern Orthodox believe the same, and the Catholic Church acknowledges that, because their Holy Orders remain valid, they have the true Holy Eucharist.
Lutherans claim “consubstantiation,” with the bread and wine not changing, but with the body and blood of Christ somehow coexisting with it.
Anglicans are, quite frankly, all over the map. Some claim real presence, through an unspecified mechanism, but deny both trans- and consubstantiation. Others deny any real presence, and speak in terms of a spiritual presence of some sort - again, there’s variations. It pretty much depends on who you read, or who you talk to.
Those are the differences in a nutshell, although there is more to the positions of each group. However, where one claims transubstantiation, another consubstantiation, and another neither, one can see why they separate at the Liturgy of the Eucharist. They are not celebrating the same thing, even though they all use the word “Eucharist” to describe what they celebrate.
Blessings,
Gerry