Sometimes it is a hassle to go find out exactly what is what on an electronic component. Here's an easy reference to always come back to to get a quick glance at what does what. Real easy, transistors have 3 leads with an emitter, collector, and base, while a mosfet has a gate, source, and drain, the opto-coupler is self-explanatory. The Hall Effect IC Chip has a supply, output, and ground.