What are some methods that UX testers use in order to test out websites?

I am curious how actual professional UX/QA testers test websites out. The reason why I ask is I have been assigned to stress-test and "break" our website for our school project, but really don't know if there's methodical ways of going about so. I've created an windows form app in the past, and when we tested it I basically just clicked on everything we created or input strings or integers into fields to try and break our algorithm, but I feel like perhaps it's different this time with our website. As an analogy, it's almost as if I'm trying to create UML-related flowcharts and diagrams, but not adhering to the UML flowchart and diagram rules, processes and the definitions of each shape.

So aside from manually going into our website and just clicking on stuff, adding values into our prompts or input fields and what not, are there actual software programs I can run that automate these sort of things? I stopped and browsed several related existing threads pertaining to the same topic, but they mention more about fundamental ways about testing. I'm looking for more specific things and possibly software I can use to help stress test our website. Thank you!