The difference is during Load and Drop of a table.
When you load data to the managed table, data is moved to the HIVE warehouse.
When you load data to the external table, data is not moved as during the creation of the table, location is already mentioned. The data in this table will be saved in the external location.
When you drop the managed table, data in the table, as well as the metadata, is being deleted. Also, it cannot be accessed from anywhere.
When you drop an external table, data is not being affected only the metadata gets deleted.