To find research articles, the general place to start will be a broad coverage database such as Scopus or Web of Science:
Use quotation marks and Boolean operators (AND, OR, NOT) to tailor your searches. For example:
lung cancer will search for the word "lung" and the word "cancer", both occurring in the same document but not necessarily near one another -- this is equivalent to searching for lung AND cancer;
“lung cancer” will search for the exact phrase;
(lung OR pulmonary) AND (cancer OR carcinoma OR tumor) will look for various combinations such as lung cancer, pulmonary cancer, pulmonary tumor, etc.
This online handout has more information about the use of these operators and other advanced search strategies.
As your research needs change over time, you should investigate some of the more specialized databases in the JOURNAL ARTICLES tab on the left; however, becoming well-versed in one (or both) of the databases above will serve you well through your academic and research career.