I took the test 3 weeks ago. My answers are for the computer version of the test.
1. Before you begin the exam, you will have a few minutes to practice on the computer get used to "navigating" within the exam. I got a few practice questions to answer and got a feel for using the computer keyboard. I found this really helpful because I was able to get comfortable with answering questions and also saw how I could flag questions, skip them, go back to them, etc.
2. Within each section (math, science, english, reading) you can answer the question, skip the question, or answer the question and flag it to go back to later. When you finish that section, you have a choice to: go back to review all questions, questions you have skipped, questions you have flagged, or a specific question number.
3. There is a timer at the top of the screen so you can see how much time remains within that section. When time runs out you must move onto the next section. However, if you finish and have time remaining you can either go back and check any questions you wish or you can opt to finish that section and move onto the next. If you do move onto the next section, you cannot go back to the previous section. If you still have time left in a particular section and choose to move onto the next section, the computer will prompt you by asking you if are sure you want to move on so you can't mistakenly go onto another section.
4. No calculators are allowed.
I hope this helps.