Here's how it works:

1. DNA in the nucleus contains the genetic code for proteins. This code is transcribed into messenger RNA (mRNA).

2. mRNA travels out of the nucleus to the cytoplasm.

3. Ribosomes in the cytoplasm bind to the mRNA.

4. Ribosomes read the mRNA code and use it to assemble amino acids into a specific protein chain.

So, the ribosomes are the protein-building machinery of the cell, and they get their instructions from the nucleus via mRNA.