The early Christians included men and women, slaves and free people, rich and poor, Jews and Greeks.
The first Christians were Jews only. They inhabited the cities of Galilee (a region of Israel). They were poor people, like Jesus, most of them woodworkers. Some were friends of John the Baptist, a great fearless prophet. All these people spoke Aramaic, a Semitic language related to Hebrew, which by those times had already been extinct (all Jews during the time of Jesus spoke Aramaic).
After the death of Jesus, around the year 30 AD, they formed a community in the city of Jerusalem, living in harmony with the Mosaic Jews. But some were contesters. Stephen, for example, criticized the Temple or the offerings of sacrifices by the Mosaic Jews and he was killed. He triggered a violent persecution against the disciples of Jesus and many left the city.
A group established in the city of Antioch in Syria. This was the place where the name Christian was used for the first time. This is also the place where the Christian Jews started to convert people who were not Jews. The non-Jew Christians were called "Greeks", "Pagans" or "Kind People". There was a problem, as the Jews were not accustomed to live together with non-Jews people. For example, the Jews followed the law of Moses, which prohibited eating with the pagans.
Still, the Christians formed groups in the large cities of the Roman Empire: Ephesus, Rome, Alexandria and others. One man proved to be very active in spreading the new faith: Paul. He was a tireless voyager and founded numerous communities, even if he risked his own life (he shipwrecked thrice!). Due to his efforts and those of others, Christians were found everywhere in the Roman Empire.
In Greek, "Jesus Christ, son of God, the saver" was written "Iesous Christos Theou Uios Soter". The acronym was Ichtus, meaning "fish" in Greek. That's why the symbol of the first Christians was the fish, not the cross.
Some spoke Aramaic, other Greek or Latin or all languages of the empire. These Christians went from poor to rich, like the Roman Lydia, the wife of a trader, who invited the believers to live in her house. Houses like that of Lydia were used for the first meetings of the Christians. They prayed, sang and tore the bread in the memory of Jesus. Rich citizens or slaves, all felt like in a brotherhood.
In a world ignorant to the human rights, the Christianity came with the idea that all are equal. Christians refused to die as gladiators in arenas or to offer sacrifices to the gods of the temples. That's why they were seen as atheist and enemies of the society, because they refused to honor the emperor. They turned into easy victims. The emperor Nero accused them of firing Rome (even if the fire had been set by slaves sent by him) in July 64.
It was the start of a violent persecution, when many Christians of the first generation, like Peter, died. But this was in vain: Christianity spread further due to its message of universal brotherhood.