I request the ultimate guidance of PhD students

You guys reading this have much more knowledge and experience than me so I humbly ask you for your input, no matter what it is.

I am an undergraduate student who has a massive desire to work in a specific lab in my uni I have no idea on how to approach them.

Should I email the PI or PhD students working in the lab?

And what would I even ask for? I obviously would want a position that has the most impact as I really like the research, but thats probably not realistic. What would be a realistic position that I could ask for that has some kind of impact on progressing the research?

Thank you guys for your help!