Hi! This is definitely THE question I faced while I was starting my undergraduate education.
As others have stated, while in undergrad, you will be required to take psychology classes related to different disciplines (abnormal psych, social psych, child psych, etc) and the topics usually become more narrowed the higher you go in course level (introductory being 100-level, advanced being 400-level). I recommend taking all of your psychology courses seriously so that you can figure out which field most interests you.
I also recommend seeking out research opportunities with psychology faculty. Conducting research in a certain area may make you more interested in that field. For example, I worked in a pediatric psychology lab where we administered a psychoeducational test, and I loved that. Turns out school psychology involves a lot of psychoeducational testing and counseling, which are two things very important to me! I would say working in that lab really opened up my choices.
Also talk to your professors during their office hours. They are specialized within certain fields/areas and you can ask them questions about why they chose their fields, etc.
Thankfully you don't really need to make a choice until your junior year of undergrad, as you will be applying the fall semester of your senior year. So if you are just starting college, you definitely have time to figure this out!
Hope that helps!