Citing your sources (a.k.a. academic integrity) is how you give credit to others for ideas that are not your own. It is very important and can be time consuming. Here are some suggestions that might save your sanity:
The following resources provide excellent examples and tutorial on the MLA citation style.
These websites will automatically format your citations into MLA style. Proceed with caution: they almost never do it perfectly. You'll still have to double check your Works Cited list.