First time going to an Onsen—what should I know?

I'm going to an onsen with my university department this Friday. I watched all the video on Youtube and read some Reddit posts but still have some questions to ask.

Is there anything I should bring with me? Also, do I stick with the group or can I explore on my own? Honestly, I'm a bit nervous, but I couldn't say no when they asked me directly, lmao.

Edit: Thank you for all the comments. I was surprised by how many I got. I'm just going to follow everyone’s advice and put my glasses outside so I won’t see anything, lol.