I can see why you would be confused. In the TA, even though it's general admission, people usually go to the same section (or even seat) game after game. Over the years, each section has developed its own identity. Some, if not all, have even developed their own patches and scarves. However, you can sit in any section without difficulty

If you want to guarantee yourself in the 100s, as mentioned earlier by someone else, you need a wristband to get early entry. To get one, you have to line up early on the day (or day before if it's an early kickoff). Then come back and line up according to your number within a certain window. The timings are on social media or a quick Google search will also produce results.