Flint and Steel is a tool that is crafted from coal and one iron ingrot as pictured above. It’s main use is to start fires but it has a few sub-uses like killing monsters, initiating portals, and destroying dropped items.
This tool is one of the main tools in a griefers inventory. They use this to set wooden homes and trees on fire which sometime causes the servers to lag and in some instances shut down. You will not want to give these away in chests near spawn to new members of your servers!