You can preview an In-Lecture Quiz by clicking Test the Quiz on the Quiz Preview page in the Quiz Generator. You can also view the appropriate lecture page in Page Builder to see what students will see. On the main lecture page for a lecture with an ILQ, sections which have an ILQ are clearly marked by the "shield with a checkmark" indicator.
When students (or you) play back the lecture section, the video will stop and the appropriate question appears at every point where you have inserted a question into video playback. Students can answer the question and receive immediate feedback, or skip the question and answer it later. A counter just below the video player tells students how many questions need to be answered to complete the in-lecture quiz.
Once a student answers all questions in an ILQ, they are asked to submit their answers so that the ILQ is considered "complete." The next time a student views a lecture section with an ILQ that they previously completed, they are asked if they want to take the ILQ again, or if they just want to watch the video without the ILQ. Students can re-take ILQs as many times as they want.