One of the challenges in doing research on topics relating to Spanish language and literature is that to find all the articles on a given topic, you may need to use search terms in both English and Spanish. Here are a couple of examples to illustrate this principle:
In cases like this, it will really save time to use Boolean Connectors. For instance, if searching for articles on Quijote's obsession with windmills, this would be a very effective search string: (Quijote or Quixote) and (windmill or molino).
When doing Author or Subject searches for individuals with Spanish surnames, generally you should use the "middle" name as the entry point. For example, to search ALICE for books by or about Gabriel García Márquez you would use this form of the name: García Márquez, Gabriel.
If the name involves elements such as De, De las, or Del, use the next part of the name as the search term. For example, to search ALICE for books by or about Miguel de Unamuno. you would use this form of the name: Unamuno, Miguel de.
These are only rules of thumb, though. When in doubt, it often helps to do a keyword search for the person's name and then see what form of the name is used by the database you're searching.
For more information, see this Wikipedia article on Spanish naming customs.
Your instructor may insist that you use all the accents and diacritics when writing in Spanish, but most library databases do not. As a rule of thumb, it is best to leave them out when doing your search.