Subject: tRNA, ribosomes, and codons

My basic question is this:  how does a free tRNA, with an amino acid already 
attached, "know" to go and bond with the appropriate corresponding codon on the 
mRNA already being processed in the ribosome?  Is it that tRNAs from the 
cytoplasm all attempt to fit, and only the one that does works, or is it more 
organized than this, using some sort of messenger chemical?  I know that each 
tRNA has a corresponding amino acid, and that they are attached outside of the 
ribosome.  My question is how the already paired amino acids and tRNAs "know" to 
go the appropriate codons at the A space in the ribosome.

Re: tRNA, ribosomes, and codons