The first translated codon is nearly always more than 25 nucleotides away. The mRNA contains signals defining the beginning and the end of the polypeptide chain. The ribosome must bind and initiate translation at the correct location or translation will be out of frame. This region is called the Shine-Dalgarno sequence. By pairing with short sequences at the 3' end of the 16S rRNA of the 30S ribosome subunit the Shine-Dalgarno sequence positions the ribosome to initiate translation.
Ribosomal subunits exist freely in the cytosol.
It has a formyl group on the amino group of methionine. It binds directly to the P site on the ribosome. This methionine is later removed in the processing of the protein. The initiating codon in mRNA is usually AUG, which codes for methionine. Hit Genetic Code for a review of the method by which nucleotide triplets code for amino acids.