How do I reference a sentence/statement that I took from the internet? Is there a certain method for it?

Its simple. For example, if an online article titled Citing Sources was written by John Smith in August 2011, and was found on the website http://ProperCitations.com and you researched it for a report on September 3rd 2011, and wanted to quote the 4th paragraph, you could cite it like this:

Smith, John: Citing Sources: [http://ProperCitations.com/Citing_Sources.html]: para. 4: [Sept 3, 2011]