Crystal structure analysis from GIXD pattern

Grazing Incidence X-ray diffraction is a popular choice for the people who works with soft matter physics, biophysics or biochemistry. I was introduced to the procedure when I start working on my PhD research project. We ran our experiment at Argonne National Laboratory. As a beginner, I struggled a lot to understand the data analysis process and how to make sense out of it. I am writing this post just to summerize the method hoping it will help some graduate student who recently start working in a similar project and having hard time to understand it. There are lots of different resources, research papers and books which dive deep into the topic. I recommend to use those resources to learn more about the process.
If you have a solid crystal, you can rotate it any orientation you want under the beam. But it is not possible for liquid substances. To put the liqud under high energy photon beam we somehow need to change the direction of the beam. In a lab, we spread the monolayer of the sample on a teflon trough. And turn on the X-ray beam. We use a monochromatic crystal to diffract the beam down to the sample. We use a 2D detector to collect the diffraction pattern rotated around the z-axis (facing upword direction).
Let's look at the top view of the system. GIXD scan covers a range of detector angle $\theta$. After collecting the GIXD data at differnt angle we combine the data by placing them next to each other using software. For me I used the LSS reader.
When X-ray shine on an object,