To get started using Code.org in your classroom or at home with your students, we'd recommend familiarizing yourself with all of our courses and their suggested age ranges for students at studio.code.org/courses, and accompanying curriculum from grades K-12 at curriculum.code.org or code.org/educate. You can also set up a teacher account to create a class section for your students, to track their progress as they work through courses.
First you'll need to create a teacher account at studio.code.org/users/sign_up, then create a section from your teacher dashboard for your students to join. You can set up class sections to allow for students to join either with or without their own email/password-based Code Studio accounts.
Once setting up a teacher account, start with this series of start-up articles for first time teachers on Code.org on finding the best course for your students, creating a class section, and adding student accounts to your section.