A phrase indicating hearsay: used to report information one has heard ("I've heard that...", "it's said that...").
明日は雨が降るということだ。
I've heard that it will rain tomorrow.
彼は来月転勤するということだ。
Apparently he will be transferred next month.
新聞によると、その店は廃業するということだ。
According to the newspaper, that shop will close down.
A phrase expressing conjecture: used to infer or judge someone's feelings or a situation ("it appears that...", "it seems that...").
あの顔つきからすると、彼は不満があるということだ。
Judging from his expression, it seems he is dissatisfied.
荷物の量を見ると、彼女はしばらく出かけるつもりだということだ。
Looking at the amount of luggage, it appears she plans to go away for a while.
返事が遅いことから、忙しいということだろう。
Since her reply is late, she is probably busy.