Heaven
noun
The kanji and the word are exactly the same. That means they share meanings as well.
Since this word is made up of a single kanji, it would normally use the kun'yomi reading. The kanji that makes this word only has one important reading, though, and that happens to be the on'yomi. Since you learned the on'yomi reading for this kanji, you've already learned the reading for this word.
きっと天にいるママからのメッセージだよ。
It's probably a message from Mom in heaven.
きっと天には、たくさんの人がいるんでしょう。
There are probably a lot of people in heaven.
あの犬、きっと天のつかいだったんだ。
That dog must have been a heavenly messenger.