Briefly (I hope), and hopefully not straining the text or the reader.

From the New American Standard Version (which is a fairly literal translation).

Acts 20:7 On the first day of the week, when we were gathered together to break bread, Paul began talking to them, intending to leave the next day, and he prolonged his message until midnight. (NASU)

Recall that this is about 3 weeks after the Jewish Passover (from verse 6; Passover + 7 days of unleavened bread + 5 days of travel + 7 days in Troas).

Recall that Paul was in a hurry to reach Jerusalem if possible by the day of Pentecost (verse 16), 7 weeks after Passover.

Nevertheless, having arrived in Troas apparently on Monday, he waited in Troas until the following Sunday, apparently so that he could meet with the church when they all came together on the first day of the week (more on the assembly of the whole church later).

Luke, the author of Acts, includes himself in the group that came together on the first day of the week.

The expressed purpose of coming together was to break bread”. That should be apparent in the English versions (we gathered together to break bread, but in case the English is not definite enough, here is the comment of Greek scholar A. T. Robertson on the grammar: "To break bread klasai arton. First aorist active infinitive of purpose of klaoo. The language naturally bears the same meaning as in Acts 2:42, the Eucharist or the Lord's Supper"
(from Robertson's Word Pictures in the New Testament, Electronic Database. Copyright (c) 1997 by Biblesoft & Robertson's Word Pictures in the New Testament. Copyright (c) 1985 by Broadman Press)

While Luke used a definite article with the expression "breaking bread" in Acts 2:42 (a participial phrase), one would not grammatically use a definite article with an infinitive (to break bread) in either Greek or English. However, in 20:7 Luke does use a "nominative" pronoun in front of the infinitive to provide emphasis (English has no direct grammatical equivalent).

"Breaking bread" is ordinary language (as is everything described in the New Testament, there is no specialized ecclesiastical language in the original) and could refer to any meal, but the emphasis and context in Acts 2:42 and 20:7 indicate that the special memorial meal of bread and the fruit of the vine instituted by Jesus is in view, a matter of devotion for the disciples, and a reason for disciples coming together on the first day of the week.

The expression in Acts 20:7, gathered together is the verb most often used to describe the gathering of the church (the church being a group of people, not a place or a building). The word can apply to other kinds of gatherings too, of course, but regarding the gathering together of the church, the same verb as found in Acts 20:7, is also used in Acts 4:31, ll:26, 14:27, 15:30, along with Matthew 18:20 and 1 Corinthians 5:4 -- assembled in the name of Jesus.

It is reasonable to conclude from Acts 20:7 and context that the church in Troas met on the first day of the week to join together in the Lord’s supper. Further, that Paul and company expected that to be the case, and adjusted their own schedule and travel plans in order to be on hand at that time. The language indicates that this was an event focused upon a particular day of the week, and the context tells us it was not based upon a particular time of year (specifically Jewish, being well past Passover and before Pentecost). Nor did the group forego their Sunday gathering for a meeting during the previous week, for Paul’s convenience, though he surely visited and met with brethren in the city during the week he spent there. This one example by itself doesn’t make a church gathering on the first day of the week a law, nor does it prove that all churches in all places gathered on that day and shared in the Lord’s supper when they did so. Nevertheless, in Acts 2:42 we have “the breaking of bread” as a matter of devotion among the disciples, and in Acts 20:7 we have a church meeting on the first day of the week for the purpose of breaking bread. And in this regard Acts 20:7 does not stand alone... but more on other texts later, as well as other supporting evidence that what happened in Troas was in fact the norm.