って

って is the casual form of three things: the quotation particle と, という ("called"), and the topic particle は. As a quotation it follows the plain form of whatever was said or thought, then ゆう言う, おもう思う or きく聞く.

Ending the sentence on って

Leave out the verb and って on its own means "I heard", "they say". With んだ in front, it is the most common casual way to pass on news.

Said louder, the same って repeats what you said yourself, because the listener did not take it in: いく行くってきごう！ "I said I'm going!". なん何だってきごう？ asks for the repeat: "What did you say?"

As a casual は

After a noun, って brings it up as the topic, often with a sense of "speaking of" or "this thing called". It is common in questions about something you know little about.

"Called"

Between two nouns, って gives the name of the second: "a manga called…".

Register

Every use of って is spoken and informal. In polite speech and in writing, go back to と, という and は.