Some of the commands in the Old Testament deal with morality, that is, what is right and what is wrong, such as murder and adultery. The commands against homosexual behavior belong to this group; homosexual behavior, like murder or adultery, is always wrong.
The other commands of the Old Testament deal with particular Jewish religious practices or customs of the Old Covenant, such as circumcision, animal sacrifices, kosher food, festivals, new moons and sabbaths.
New Covenant Christians are no longer bound to keep Jewish religious practices or customs of the Old Covenant, as can be seen from chapter 15 of the Acts of the Apostles and Colossians 2:16-17. Christians, however, are still bound by the moral commands of the Old Testament because what is right and what is wrong does not change; murder and adultery are always wrong.
How do we know what is an unchanging moral law and what is a changeable custom? We must trust the hierarchical Church instituted by Jesus Christ to determine such things, as it did in Acts 15.