How to follow and contribute to a research discussion when less experienced?
Don't worry about it. You're a second-year PhD student, so you're one of the least experienced people in the room. Everyone should find this reasonable. What matters is that you show a willingness to learn, to grow, to understand, to improve.
Don't be afraid of asking questions. Don't even be afraid of asking stupid questions. Most scientists will gladly elaborate if you show a genuine interest in understanding the topic better.
Study the topics in your field. Deepen your understanding in your own PhD topic, and adjacent topics on which other people at your conferences are working. If you keep working on improving your understanding, you will notice that over time, you will be able to keep up with the pace. The key is to not panic that you're not there yet, but instead display that you are willing to learn.