How to talk to other UG researchers and/or PG researchers?
In my experience, researchers who are genuinely interested in the same topics as you will be happy to discuss them regardless of whether you're at the same stage of education. Push yourself to attend events that challenge and inspire you, whether they're mainly attended by graduate students or by undergrads, and don't tell yourself that you're an intruder there. Most people won't be thinking about whether you're an undergrad or a postdoc; they'll just be listening to the ideas you exchange. As a graduate student myself, I love working with undergrads who are motivated and excited about research. Of course there will always be some people who think they're above you simply because they have more credentials, but that's their problem, not yours.

Asking people about their own  research can be a great entry point since everyone likes to feel that what they're doing is appreciated. Check out a poster session on campus and find a few posters that you're interested in. Eventually you'll start a great conversation with someone. Be patient and don't give up!