The GRE General Test begins with the AWA Section where you have to write 2 essays based on the given issue and argument. 30 minutes are given to read the issue/argument and write an essay based on it. These essays are graded on a scale from 1-6 and the average score is rounded off to give the AWA Score.
The AWA section is followed by 2 Quant Sections, 2 Verbal Sections and 1 Experimental Section which can be either Quant or Verbal. The Experimental Section is not scored and not revealed during the test as it used to improve the pool questions used by ETS for students appearing for the exam all over the world. Since you end up solving either 3 Quants sections or 3 Verbal sections, you know that one of those was experimental. These 5 sections have a section-wise adaptive difficulty i.e. if you perform well in a Quants section, the next Quants section will be slightly more difficult. Also, a Quants section is followed by a Verbal section and vice-versa.
Each Quants section has 20 questions and 35 minutes are given to solve them. Whereas each verbal section has 20 questions but only 30 minutes are given to solve them. You cannot go back to a previous section while answering the questions but you can browse through all the questions of your current section. Once the time limit for a section is over, all the questions are submitted automatically.
The GRE score is a relative grading score on a scale from 260 to 340. Yes, you cannot get less than 260 on the GRE. ETS uses a complex algorithm to compute the Quants and Verbal scores wherein each question is graded based on its difficulty. Which means getting a very simple question wrong affects your score a lot but getting a complex question wrong will not have much of an impact on your score.