My course wasn't physics related, but I did have lots of labs! In my experience, labs were nothing like that. In first year especially, we were given detailed instructions and there was lots of assistance on hand! For one module (microbiology related) we were expected to read up on the labs before hand- I guess if you didn't do the reading, you would end up being stuck.
However, there will be guidance and help available, and most of my first year work was done in small groups, so if you don't understand everything, you can help each other.
It's not really until you're doing your dissertation that you might face being in a lab with no-one guiding you as to what to do.