Selecting a thesis advisor is a very ad-hoc process that is largely incumbent on the student to move forward.  The two most important factors in picking an advisor are:

• Can I work well with my advisor during a year-long project?
• Is the advisor an expert in my thesis topic?

Students typically start by asking professors they have worked with previously, either in class or as part of a separate research project.  This approach works well if you have already been on campus a quarter or two.  If you haven’t meet any professors yet the best approach is to reach out to them via email.  The CSSE department’s list of faculty and research interests is available a https://csc.calpoly.edu/faculty/.