When using a person's work, be it a line you want to make use of from the original work, knowing that you are using someone else's work, you use quotation marks ("") at the beginning and end of the copied sentence. That way you are passing an information to the reader that you have borrowed this line and not plagiarized.
An example "what is worth doing is worth doing well"

As for citation goes down to showing the source to the reader, that is, citing the source of where your material is from

I hope you do understand this.