stress test is a test where you apply load to all parts and discover if they run well or not
any gpu test like unigine heaven or valley, gfxbench or cinebench applies pressure on cpu, gpu, ram or all of them in some form, that is a stress test, to get performance results, that you can use to compare against other peoples machines and decide if your pc is performing well enough compared to the other similar pcs or if you can do changes and get better results
i do that regularly to see if i have made bad changes to bios, any overclock doing weird stuff or see how things keep performing over time
a better question would be, what hardware do you have and what has you worried you about it?
problems running a specific game? do you feel it...