how do ribosomes in cell act as factories for protein synthesis ?

 
Ribosomes in cells act as factories for protein synthesis. They are the workbenches for translation  (protein production form mRNA). Ribosomes have 2 subunits: a large subunit and a small subunit.Smaller subunit comes in contact with mRNA to initiate the process of translation. Then t-RNA-amino acid complexes bind to their corresponding codon on the mRNA and base pairing occurs between codon on mRNA and tRNA anticodon.
tRNA moves from codon to codon on the mRNA and amino acids(attached to tRNA) are added one by one. Amino acids are polymerised to form a polypeptide of protein. Complete polypeptide chain is released from ribosome when stop codon is encountered on mRNA.  In this way, proteins are manufactured on ribosomes.