Slader

Slader is an academic community for students, by students. It is the first crowd-sourced approach to education online. Slader empowers students to shape their own educational experience.
Users view and share original answers and work for high school textbooks, join academic classes, post homework assignments, and discuss subject-specific questions with their peers and classmates on the Slader site. Slader offers an alternative to expensive tutors and costly after-school programs. It ensures that every student has access to the academic resources that secure success.
This free website has information for all classes and text books, but I've only used it for math homework. It is very helpful, and explains the process of solving problems step-by-step.