The contribution in the very early years (Acts 2 - 7) went to address the needs of the local Christians. These earliest Christians were "voluntary communists", dividing their possessions among each other so that none had need (Acts 2:44-45; 4:34-35).
It was voluntary, not compulsory (Acts 5:4).
Later, when hard times hit the saints in Jerusalem, the Gentile Christians in Antioch took up a collection to send to the Jewish Christians back in Jerusalem, via Paul and Barnabas (Acts 11:27-30).
When the Jewish leaders there asked Paul to help, he was glad to do so (Gal 2:10). He began a fund-raising effort among the Gentile churches in Macedonia/Achaia/Galatia/Corinth; the basic instructions are found in 1 Cor 16:1-2. This was a year-long fund-raiser, with a definite start and a definite finish (2 Cor 8:10-11), and was not a command but an appeal (2 Cor 8:8), and was designed to bring parity between the Haves and the Have-Nots, with the expectation that should the situation reverse, such that the Jerusalem church prospered and the Gentiles were needy, the flow of money would also reverse, to go the other direction (2 Cor 8:13-14). Paul did not expect a contribution from those who didn't have (2 Cor 8:11-12), but only from those who had prospered (1 Cor 16:2).
In addition to this contribution for the financial equality of all Christians, Christians are expected to support themselves (Gal 6:5; 2 Thess 3:8-10), to support their own family (1 Tim 5:8), to have a job so they can help the needy (Eph 4:28), and lastly, to support the spread of the gospel, via paying preachers/missionaries/etc (1 Cor 9:1-14; Gal 6:6; 1 Tim 5:17-18).