system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Transistors, what they do, how they work, how they're used.
gpt
Think of them as a valve. You have a flow through them, which you can turn on or off with another, much smaller flow.

Now, how can we do so much with this:

Well, there are two cases: analog and digital.

**Analog:**

You don't have to open or close the valve all the way. This means that you can use a small flow (a weak signal) to regulate a much larger flow (a strong signal). This, basically, is an amplifier. You use a weak audio signal to control a much larger current through the transistor, driving a set of loudspeakers. Of course, an audio amplifier is just an example, they are very useful in other applications as well.

**Digital:**

In this case, we only use the valve as an on or off. So, basically, we have a tiny, tine swithc which is operated by an electric signal.

Now, you think, "What's the use of that?". Well, almost nothing. However, you can connect this with other switches. many of them, billions of them, creating a network (not network as in "computer network") of switches that can actually do things. By arranging them cleverly, you can set groups of them up as memory cells, you can add numbers in memory cells, you can move stuff between memory cells and so on. Do this cleverly enough, and you've got a computer. That's pretty useful.