terraria how to make a good weapon?

Answer 1

There are weapons that can be found in chests located in caves and dungeons. Usually, the best weapons are made from demonite (found from bosses), meteorite (found when one lands at night [make sure you have an obsidian skull equipped]), obsidian (lava that has been put out by water), and hellstone (found in the underworld)

You will also need a hellforge which acts as a furnace to create hellstone bars and armor/weapons, but if you have one, you can just toss the old furnace away.