en_tn/jhn/02/13.md

up to Jerusalem

This means that they traveled from a lower place to a higher place. Jerusalem is built on a hill.

in the temple

This refers to the outer courtyard of the temple where the non-Jewish people were allowed to worship.

those that sold

People could buy animals at the temple and sacrifice them to honor God.

money changers

Jewish authorities required people who wanted to buy animals for sacrifices to exchange their money from outside for special money from the "money changers."