Protein trafficking in the endoplasmic reticulum involves the folding of the protein, tagging it with the intended destination, and releasing the protein.
The protein may be released to the Golgi apparatus, where it can then be transported through the cell by membrane trafficking. This allows the secretion of the protein extracellularly, using a series of nudges to target the protein to the correct destination. Where a protein is misdirected, recycling the protein through the transport network allows it to reach the correct destination a second time around.
Proteins are tagged with their destination (normally) on the N terminus, allowing the cell to easily determine where to direct the protein. Proteins with similar destinations are grouped together into the same vesicle, improving the efficiency of the transport process.