Research builds on previous research. To avoid repetition and find gaps and opportunities, literature review/search is crucial.
Before you head to literature review, you need to find out relevant articles. Reading these articles you may understand what has been done so far in your research area. Before reading you need to find out first the relevant papers. Some possible sources:
1. Google Scholar ( https://scholar.google.com/)
2. PubMed ( https://www.ncbi.nlm.nih.gov/pubmed/)
3. DOAJ ( https://doaj.org/)
4. NepJOL ( https://www.nepjol.info/)
You may also visit Research4Life ( https://www.research4life.org/) and look at their different programmes to help researchers.
A recently published review article in your research area can save your time to look at literature. You may also see all the references that may help to get a research gaps.
Which journals to read?
You need to know which are the most well established journals in your area. You may also ask to your research advisors. You may also query/discuss in ResearchGate ( https://www.researchgate.net/)