What it means
ということだ reports information that the speaker learned from another source. It commonly follows a plain clause and means “it is said that” or “I heard that.” The speaker presents the information as hearsay rather than as a personally confirmed fact. The form can also mean “that means” in a different context, but the hearsay meaning is especially common when it follows a complete statement.
Usage note
In formal writing and polite speech, ということです is the natural polite counterpart. Do not confuse the hearsay use with the explanatory use of ということだ, which can mean “that means” or “in other words” depending on the context.
How to use it
来月、駅前の店が閉店するということです。
I heard that the shop in front of the station will close next month.
来月、駅前の店が閉店するということだ。
I heard that the shop in front of the station will close next month.