Schoology is a learning management system. It is designed to help teachers store files, share content, post assignments and quizes, and keep grades. It brings together all of the educational content a teacher may want to use online and puts it in one place.
Schoology connects with different popular apps like Google Drive, Google Classroom, YouTube and many other apps. You can easily create materials, share it with others or browse materals others have created.
It is easy to create test questions, randomize their order, have the tests automatically graded and scores stored into your gradebook. They even have a highly functioal mobile app that will work with all of your Apple or Android devices.
If you are a teacher and you only use one website online, I'd make it schoology.