Exocytosis is basically when your vesicles transport materials out of a cell.
Once the neurotransmitters are synthesised and packaged into vesicles, they are transported until the vesicles reach the cell membrane. Then the 2 bilayers rearrange themselves so that the vesicles are able to fuse with the membrane . Once that occurs, the neurotransmitters will spill out whatever it was carrying.
Two examples of exocytosis are
1) your nerve cells releasing transmitters (explained in the description above)
2)your T cells sending vesicles filled with enzymes to viral infected cells
