How is congress involved when the president negotiates a treaty with another country?

In the United States, for an international treaty to have operational capacity it must be ratified by Congress. That is, Congress gives it the force of law, and from that moment the treaty applies to American citizens. Thus, although the President is the one who negotiates and signs the treaties, the Congress makes a sort of revision and approval of the signed treaties.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.