b.In some contexts, I am not sure to use it or they.
For example, when my friend is polishing the spoons and the forks (it is in the restaurant), I have to ask him when it/they will be ready. (they are referring to the spoons and forks), whereas (it is referring to the cutlery). Because your friend, in that situation/context, is handling multiple pieces of cutlery I would expect to hear/use "they". However, I would use the actual term (cutlery) rather than "it" if you wanted refer to the variety of pieces.
On other hand, let's say I am trying to put the two sides of a box together. Here comes my daughter and she is trying to help me out.
I say,' put it/them together.' (again it is referring to the box) (them is referring to the 2 sides of a box).
Please tell me which one is more appropriate. I would be very grateful if you can explain a bit as I am sure there are so many people are confused as me about it/they uses in these situations. I would use and expect to hear "it" because you are referring to assembly of the box and not to the sides. If you wanted to refer to the sides in particular, I would say something like, "Put the sides in place".