Proteins are built during TRANSLATION.
During translation, the information to build the RNA comes from messenger RNA (mRNA)
mRNA gives instructions to amino acids on transfer RNA (tRNA) to come together in the ribosome containing ribosomal RNA (rRNA).
The amino acids form a chain called a polypeptide (proteins are made up of one or more polypeptide chains).
I have attached an image of the process of translation to help improve your understanding.
I hope this helps! I'm happy to help with any other questions you might have :)
[Image sourced from: http://ib.bioninja.com.au/standard-level/topic-2-molecular-biology/27-dna-replication-transcri/translation.html]