Did Jesus start a new religion called Christianity?

No. Yeshua (Jesus) and His first followers never thought of themselves as starting a new religion. They were Jews, keeping the feasts, praying in the Temple, reading the Hebrew Scriptures. They believed they were watching the God of Israel keep a promise He had made to Israel, not founding something brand new.

The institution we call Christianity, with its councils, creeds, and separate calendar, was assembled centuries later, largely under Rome. That is the part that was built by men.

The faith itself was not invented by a founder or voted on by a committee. It came straight out of the text, and it was already there long before anyone called it Christianity.