This is usually the order in which the sections appear:
Reading, Listening, Break (10 minutes), Speaking, Writing. The passages are usually not more than 700w in length and have academic subjects but should not be very difficult after a little practice, especially if you are used to GRE/GMAT passages.
The atmosphere in the room will vary depending on where you take the test. Which city/country are you from? In India, the test in usually conducted in colleges, so there can be some background noise/disturbance etc. However, the headphones are generally of a good quality.
Hope this helps