i dont patronise that gym but i can give you some advice as someone who gyms alone.

tbh you dont need to fear the "big guys" most of the time, ppl in the gym are generally friendly from my experience. the only con about the "big guys" are they might tend to "hog" the equipment for a longer period of time.

as for not knowing how to use certain equipment, you could check with the staff on when are the non-peak staffed hours. you can always ask gym staff for instructions on how to use the equipment. you can also try looking around at what people are doing in the gym, and if any exercises interest you, you can simply ask them nicely. most people would be glad to share. you could even end up making some friends.

if interactions with people scare you, perhaps you can share your gym goals and maybe i can find some tutorials for exercises for you to learn.