Create a free teacher account at socrative.com; log in. Students do not need to create accounts. NOTE: These apps have been updated and look slightly different now, but the steps should be the same.
Note the code/room number you are assigned (top right). Your students will use that number to answer your questions. You can ask Multiple Choice, T/F, or Short Answer questions from here.
This is what the student app or the mobile site (m.socrative.com) looks like. Students don't have to log in or register; they just enter your room number to answer your questions.
Once you pose a question (you can just say it out loud; you don't have to enter it anywhere), you can wait for real-time results as students respond.
If you do want to type out a question, you can choose different options for your students' responses.
You can also create or import quizzes and choose advanced options.
The quizzes you create stay in your account for future use.
Socrative also has an exit ticket you can use. Your students will see 4 pre-made questions (listed at the top of the screen.)
Besides viewing the results in real time, you can have a report of your students' responses sent to your e-mail. The feedback is instant, and it's extremely user-friendly for students and teachers.