Welcome to Magoosh! :D
If you're brand new to the GRE, you should definitely consider following one of our study schedules. They're detailed, step-by-step guides that will take you through exactly what to do to in order to dominate the GRE :) If you're not sure which study schedule is right for you, take this short quiz to find your perfect study plan.
If you decide not to go with a study guide, then the best way to use Magoosh is by going through the lesson videos, one module at a time, and doing the practice quizzes at the end of each section. We recommend that you watch the lesson videos in the order in which they're listed on the Lessons page: start at the top and work your way down :) You should work through Verbal and Math at essentially the same time. You might study Math one day, Verbal the next, and so on :)
As you go through the lesson videos and finish each section, you can create custom practice sessions with the Practice tab. Set the filter to show the types of problems that you learned in that section and use it to review subjects that you've studied before. If you're having trouble applying the concepts that you learned in the lessons to the practice questions, you can set the difficulty level to 'Easy' and practice those first. Make sure to watch the explanation videos for the practice questions, too — there's a lot of useful tips and strategies there :)
You should also check out our eBooks (especially the vocabulary one):
Check out our GRE blog as well. It has tons of articles with specific strategies, study tips, and extra practice questions.
Best of luck! :)