The first two sentences of the Wikipedia Ribosome article say:
The ribosome... serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules.
Slightly later, in the Overview section it says:
Ribosomes can bind to a messenger RNA chain and use its sequence for determining the correct sequence of amino acids for generating a given protein. Amino acids are selected, collected, and carried to the ribosome by transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA chain. It is during this binding that the correct translation of nucleic acid sequence to amino acid sequence occurs.
And it then tells us "The attached amino acids are then linked together by another part of the ribosome."
So, the function of the ribosome is to make sure each codon of the mRNA is matched up with the correct tRNA, and then to catalyze the linkage of the associated amino acid to the growing chain of the protein being built.