Usually, you are finished locating and using information when you:
1. have searched each of the sources you selected as potentially useful information sources for your topic
2. feel sure you have enough information to answer your essential or focus questions
3. find that your information is becoming repetitive
4. have collected notes that will support each section/subsection of your outline (for a paper or presentation.)
At this point, make sure that the information you have located meets all of the requirements of your assignment (refer to your rubric!) Specifically, the information should support or prove your thesis statement. If you are not sure, check with your teacher.
The locating and using parts of the research process are often iterative. This means that you may find articles or books or web pages on your topic, read and take notes from them, decide that you need more information and go back to locate more sources of information, thus repeating the process several times until the above conditions are met. Don't stop too soon or just because you have the "suggested" number of notesheets - make sure you have enough information to successfully present your research in a meaningful and convincing way.