There are a number of citation styles used in scholarly writing. Your assignment may specify which one you should use, or let you choose for yourself. If you're not sure, check with your professor. The most commonly used styles are:
There are comprehensive lists at the Purdue Online Writing Lab (OWL) and Wikipedia. Also look at:
It is important to cite your sources for many reasons:
Barns, Bill, and Gene Ambaum. "Unshelved." Comic strip. Unshelved. April 16, 2012. Accessed August 31, 2017. www.unshelved.com
Citation generators create the citation for you.
CAUTION - generators are not magic, they require YOU to enter the title, author, publication info, etc into the form. Make sure to spell everything correctly and check the generated citation against a style guide to insure your citation is correctly formated.