Tortilla Flat follows a group of aimless, jobless friends in Monterey, California, just after World War I. Danny, who has inherited two houses from his grandfather, spends his days drinking and giving things away to his friends, who never pay him back. The story contains many overt parallels to the legend of King Arthur and the knights of the Round Table, and is primarily concerned with the bond formed within the group of loyal friends.
The most popular website for book notes. SparkNotes was created by students for students, and their summaries are accessible and extremely well-written. Besides the usual plot overview, chapter summaries, and character analysis, SparkNotes differentiates itself with a section discussing themes, motifs, and symbols.
Their book summaries aren't as good as other providers, but PinkMonkey often has interesting insights that aren't mentioned elsewhere on the Internet. For example, they go over literary elements (like setting, conflict, and mood), compare and contrast, and symbolism/motifs. It's a good site if you want to find a unique fact or angle that other students don't know about.