Go to https://socrative.com/ and click on Login to sign as a student. Students don't need to create an account so they can connect to teachers quickly.
Students will need to enter the room name provided by the teacher. Enter the room name and click Join to login.
If the room is private, students will be required to enter their Student ID before clicking Submit. The IDs are created and provided by the teacher; if the Student ID doesn't match one assigned to a student in the particular room's roster, they will be unable to log in.
As students join the teacher's room, they'll be able to participate in all of the activities that are launched until they log out. If there's no activity running, the message below will be shown:
Here's a guide for teachers on how to launch a quiz. Once launched, the quiz will automatically start for the students!