There are many, many types of BJTs out there, and most of them are interchangeable with each other for the vast majority of projects, as long as you match types properly. That means that the parts list is totally up for interpretation according to what you happen to have in your parts bin at home.

You will need -

+ NPN and PNP type transistors. For the sake of these demos I will be using 2N3904 (NPN) and 2N3906 (PNP) for nearly everything as these are extremely easy to get your hands on. Any differences will be noted. 2N2222 BJTs can be used for the 2N3904 and 2N2907 can be used for the 2N3906 if needed.

+ various resistors - a range of values from 100-100kΩ will work nicely. Exact values will be given as needed.

+ other bits - LEDs, motor, speaker, flex sensor, electret microphone, audio transformer, etc. Basically components that require some amplification to be useful, or require more power than the circuit can provide. Some of these will be used, others are suggestions for your own projects later on. Details will be given in the demos.

+ breadboard - none of these demos is meant to permanent, so get a breadboard for ease of building

+ jumper wires - for connecting bits together

+ 9V batteries and battery connectors - for power

Images 1 and 2 are diagrams for both types of BJTs - NPN and PNP. The three pins are labeled as Base, Collector, and Emitter (FYI - for FETs, these are labeled Gate, Drain, and Source and serve the same functions). Carefully note the orientation of the three pins in the image 3. Datasheets are your friend and will save lots of headaches. Always double check the datasheet for the BJT you are using since some use a different pin configuration. I'm always getting the pins crossed anyway, which for most projects won't be an issue if you catch it quickly enough, but it's best to avoid it. Here are the datasheets for the 2N3904 and for the 2N3906.

As always there is a lot of information on the datasheets. Pay special attention to the maximum ratings. Don't operate near max ratings if you can avoid it, always giving yourself some room. Now look at image 1 again. In order for NPN BJTs to work, the base voltage (Vb) must be more positive than the emitter voltage (Ve). And the collector voltage (Vc) must be more positive than Vb. Going back to the max specs for the 2N3904 from the datasheet, we see that if Ve is 0, Vb can be no more than 6V more positive than that. And Vc can be no more than 40V more positive than Ve. Vb must be somewhere in between Ve and Vc for the BJT to work. The Vb threshold for many BJTs is about 0.7V, meaning that at that voltage they begin to open. Also, the nature of BJTs is that while you will need a minimum of about 0.7V to turn it on, the current through the base is the defining factor for performance. As the base current increases, so does the collector current. This is different for MOSFETs, which work more on gate voltage than current.

For PNP BJTs to work, reverse all of that from above. Vb must be more NEGATIVE than Ve, and Vc more NEGATIVE than Vb. A little trick to help remember is to remember the type you are working with. NPN require Positive voltage and current, and PNP require Negative voltage and current.

BJTs need to be protected from too much current, just like any other component. Don't ever connect the emitter and collector pins directly between the power supply and GND. Always put a component with resistance in series. Going back to the 2N3904 datasheet, we see a max collector current rating of 200mA, but in the bullets under features on the first page it says 100mA. That is an ideal figure and it's not a bad idea to use that as a self-imposed max value. Again, stay away from max limitations by using resistors. Obviously we will be operating at much lower than max for these demos.

Image 4 shows a different type of packaging for BJTs. The smaller package, like in image 3, is known as the TO-92. The larger style is the TO-220. These packages are used in many applications besides BJTs and FETs, so don't assume that since it looks like one, it is one. Always check your part numbers. The difference is that the TO-220 can handle much, much higher current loads than the TO-92 if properly paired with an appropriate heat sink. I have some that are rated for 30A as opposed to 0.2A. There are still many more types of cases for transistors, if you're interested, and you can even get them as arrays in an IC package on one piece of silicone, like the LM3046.