mRNA is the copy of the complementary strand of DNA. It forms when the DNA helix unwinds, hydrogen bonds between the strands break and then free nucleotides pair up to their complementary bases on one strand of DNA. This making of mRNA is called TRANSCRIPTION.
rRNA is what makes up the ribosome (this is the organelle in which protein synthesis occurs AKA TRANSLATION).
tRNA are the free molcules which are found in the cytoplasm. They have an attachment site in which amino acids can join onto (with the help of ATP energy).
When a specific CODON (triplet of bases) on the mRNA is read in the ribosome, the ribosome triggers for the correct tRNA with the complementary ANTICODON to the CODON to come and link up with the codon in the ribosome.
This process of calling a tRNA molecule continues, and it is when there are 2 tRNA molecules in the ribosome next to each other that a peptide bond can form between the two amino acids (which are still attached to the other end of the tRNA molecules). This goes on until a STOP CODON is reached on the strand of mRNA which is being read in the ribosome, which then STOPS this synthesis.
Hope this makes some sense!