When you are writing an academic paper, you should use scholarly sources. One way of doing that is to use peer-reviewed journal articles. See the following video for more information: Peer review in 3 minutes.
You can limit your search to articles from scholarly peer-reviewed journals in some databases. However, if you do that, other types of scholarly publications are excluded, such as academic books and dissertations.
It is good to always check that sources are scholarly. Here are some things that characterize scholarly literature:
The author should be affiliated with a university. If it is a journal article, author affiliation is often stated on the first or last page of the article. In some databases, that information is also included in the record of the source. If it is not stated in the publication or in the record, you can try to find information about the author on the web or in ORCID (a database containing information about researchers).
The publication should contain a substantial number of references (primarily scholarly sources).
The writing often features terminology specific to the field of study.
Scholarly articles are typically considerably longer than articles published in popular magazines, which are usually only a few pages.
Academic books are also distinguished by being published by university presses — such as Cambridge University Press, Harvard University Press and Sorbonne Université Presses — as well as other academic publishers like Routledge, Bloomsbury Academic and L'Harmattan. If the publisher is not a university press, you can consult the publisher's website to verify that they produce academic literature.
Student theses are usually not considered scholarly publications in the strict sense, since they are not reviewed by researchers who are experts in the field, among other things.
Even if it can help to find high-quality literature by using scholarly publications, you should critically evaluate all sources. Authors can for example be biased and exclude information that does not support their views. Consequently, check what other authors have to say about the same subject, if possible.
Unfortunately there are many articles on the web from so called predatory journals, which are low-quality and dishonest publications. Predatory journals make money by deceiving researchers into believing that they are legitimate scholarly journals and charging authors a publication fee without checking articles for quality. They also usually falsely claim that they are peer-reviewed journals and sometimes the editorial board consists of people who do not exist or who are unaware that they are listed as members of the board.
If you are using the MLA International Bibliography and the Linguistics Collection, the risk of encountering articles from predatory journals is very small, In contrast, searching in Google Scholar carries a much higher risk. If you use other search tools than the MLA International Bibliography and Linguistics Collection, you should always check that open-access articles are not from predatory journals (check on the journal's website if it is an open-access journal). One way of doing that is to check if the journal is listed in Cabells Predatory Reports. If the journal is listed in Cabells Predatory Reports, it is advisable not to use articles from that journal. Even if Cabells Predatory Reports is continuouly updated, there may be some predatory journals that have not yet been identified and included in Cabells Predatory Reports. It can therefore be good to use other methods and resources to check that it is not a predatory journal. For example, you can check if the journal is indexed in Journal Citation Reports. If the journal is indexed in Journal Citation Reports, it should not be a predatory journal. You can also check the Norwegian Register for Scientific Journals, Series and Publishers. If a journal has been approved in the Norwegian Register (i.e. if the journal has been classified at level 1 or 2), it should not be a predatory journal. You can also check if the journal is indexed in DOAJ (Directory of Open Access Journals). If the journal is indexed in DOAJ, it should not be a predatory journal.