John Gill Commentary Acts 2:4

"And they were all filled with the Holy Spirit, and began to speak with other tongues, as the Spirit gave them utterance." — Acts 2:4 (ASV)

And they were all filled with the Holy Ghost
With the gifts of the Holy Spirit; they had received the Spirit before, as a Spirit of grace, and were endowed with great gifts; but now they had great plenty of them, a large abundance; they were like vessels filled to the brim; they were as it were covered with them; there was an overflow of them upon them; and now it was, that they were baptized with him; (See Gill on Acts 1:5).

Not only the twelve apostles, but the seventy disciples; and it may be all the hundred and twenty, that were together, even women as well as men: (Acts 2:17Acts 2:18) .

And began to speak with other tongues ;
besides, and different from that in which they were born and brought up, and usually spoke; they spoke divers languages, one spoke one language, and another, another; and the same person spoke with various tongues, sometimes one language, and sometimes another. These are the new tongues, Christ told them they should speak with, (Mark 16:17) such as they had never heard, learned, nor known before:

as the Spirit gave them utterance ;
they did not utter anything of themselves, and what came into their minds, things of little or no importance; nor in a confused and disorderly manner; but they were wise and weighty sentences they delivered, as the word signifies; even the wonderful works of God, (Acts 2:11) the great doctrines of the Gospel; and though in different languages, yet in a very orderly and distinct manner, so as to be heard and understood by the people. The Vulgate Latin and Ethiopic versions read, "as the Holy Spirit"