How C. Elegans is used for siliencing genes
From the way that you have described your experiment, feeding C.elegans bacteria that are expressing a plasmid that will induce gene silencing, then both @Kendall and I think that you are likely performing an RNAi (interference) experiment.
As @Kendall writes:

If it's what I'm thinking of, you probably have GFP+ worms that end up getting fed some
DH5-α E. coli that were transformed using CaCl2. The outcome is your control worms should nicely fluoresce, and the experimental worms will be a noticeably weaker color. The RNAi process is explained nicely in that link provided by AMR. –  Kendall

The bacteria will transcribe RNA molecules encoded by the DNA plasmid. These RNAs will have complimentary sequences to sequences from your gene of interest.
When the nematode eats the bacteria, they RNA molecules that the bacteria has produced will be taken up by the cells of the worm.
The Dicer enzyme then cleaves the dsRNA into small fragments. These fragments are then able to hybridize with the mRNAs transcribed from the gene of interest. This will either cause the ribosomes not to bind properly or will start translation out of frame or without key amino acids or will terminate translation early.
The net effect is that the cells will either not produce the protein encoded by the gene of interest or will produce a non-functional protein. If, as @Kendall said, the gene of interest is a reporter gene such as GFP, then the result of the interference experiment will be C.elegans that do not fluoresce. If the gene of interest is a structural protein such as actin, then you will see the effects of knocking out the actin gene on the cells of the worm.
This online video protocol from JoVE.com gives a detailed overview of the RNAi in C.elegans experiment and also demonstrates how the protocol is carried out.