Going off of what I remember.... :D
mRNA: AKA Messenger RNA, this RNA gets to be translated into a protein.
tRNA: AKA Transfer RNA, plays a role in translation of mRNA into a protein...recruits amino acids to the ribosome where the protein is growing.
rRNA: AKA ribosomal RNA, makes a part of the ribosome, a protein RNA which is also involved in the process of mRNA into a protein.