You may be wondering why I have included a video of my business card on the website. It's on the site because I designed the business card to be a type of small interactive exhibit, the card is a demonstration on how transistors work. The user can also experimentally use the card in different environments to see the effects the environment has on transistor circuits. Transistors amplify current. Let's take a moment to define current; in our definition current will be flowing though a wire. In a simplified way current is the number of electrons (the particles of atoms that flow through the wire) that pass though a cross section of wire within a given amount of time. Current is measured in amps, and one amp is equal to about 6.24*10^18 (or about 6,240,000,000,000,000,000 electrons; this also gives you an idea as to how small electrons are) electrons passing through our cross section of wire in one second. One amp is relatively a lot of electrons, to put it in perspective your home outlets will only let you use 15 amps.
The introduction of a small amount of current into a transistor alters the material within the transistor. The material within the transistor essentially becomes more conductive allowing more current to flow through it, thus a small amount of current into the transistor allows a large amount of current to flow thought the transistor. So when I touch the business card a small and imperceivable (I can't feel it) amount of current flows from the battery into my fingers and out to the transistor. Upon entering the transistor the small amount of current makes the transistor more conductive, allowing a greater number of electrons to flow through the transistor. This greater number of electrons passes thought the light making it glow.
To clarify the silver circles are very thin batteries connected in series, which just means they are connected in such a way that one can think of them as one single battery. The little black rectangles with two silver sides are resistors, check out this project for a bit more information about resistors. The yellow rectangle is a LED (light emitting diode), it's sort of like a really efficient light bulb. There are also two transistors inside the blue square. You can think of it as one transistor amplifying the current a little and the other transistor amplifying the current some more, so the combined result of all that amplification is more current than one transistor could amplify on its own. The two transistors attached like this are effectively treated as one transistor, so from here on out I will just pretend the blue square is one transistor. When I touch the two "touch" spots on the card a small amount of current (small arrows) travels from the negative battery terminal (violet square with red boarder) through the transistor to my finger on the "touch" pad (on the back of the card) then through my hand and to the other finger on the positive terminal "touch" pad (on the front of the card). When the small amount of current travels though the transistor it alters the medium of the transistor and allow it to conduct more current (big arrows). Now that the transistor can conduct a lot more current, most of the electrons travel from the negative terminal through the transistor then through the light and to the positive terminal. The violet squares outlined in red and the red circles simply indicate where I have drilled holes though the card allowing current to flow through the card.
I should mention that this diagram shows electrons flowing from negative terminals to positive terminals. If you look at electronic schematics (it's just a fancy name for diagrams of electronic parts) you get the impression that things should be reversed. This is because scientists pretty much guessed which way electrons flowed, then made schematics before they could test to see if they were correct. Unfortunately they were not correct, but it doesn't really matter that much because it doesn't matter which way electrons flow, positive to negative or negative to positive, current still behaves the same way.