The liaison librarians for your subject areas have created guides which showcase the best search tools for you.
Dictionaries help you understand what words mean.
Thesaurii help you find words that have the same meaning.
The guides for your subject area will also list specialist reference sources.
To find what is available in your discipline, you could try the following keyword search strategy (substituting the relevant discipline for the engineering example here):
You can also use Wikipedia for background, but be aware that it is not an appropriate source to cite in your academic research. Start by searching the library catalogue and reference sources
Need suggestions for creating a search? Have a look at the Plan section of this guide.
Finding more resources about the same subject