In its most basic form, it is a plastic board covered in fibreglass. Components are mounted on a non-conductive board and connected with small pathways, called traces. These traces allow the electrical components across the board to function by passing electricity through.

This actually helps a lot thank you

You start by having a fiberglass and resin board, that has copper foil "glued" on it. Then you remove the unnecessary copper (etching it) and you are left with copper that you need. Copper forms "wires" called traces, that are used yo connect components. Then you solder components to ends of these traces.

Ever see something wired up with electrical wires and there is just bundles of crazy wires all jammed in together and you wonder how you would even know what each of those wires even does? A circuit board is just a way to connect all those tiny components with tiny little electrical connections. The real magic is how they create them to efficiently utilize the least amount of space. Like packing a ton of stuff in a little suitcase. Imagine you had an electronic that had dozens of little electrical components to connect together. If you start using wires it quickly becomes a mess no matter what you do. Those little circuit boards can connect all the little parts with little space, and better than that they can basically be printed out with machines and cut to shape and heated up and all the little chips just get shoved into their tiny holes and get soldered into place. You can wire tons of stuff together in a tiny space just by making it small enough and finding the most efficient way to connect them together that uses the least amount of space or fits a shape that the circuit board needs to fit into.

I think the most interesting thing about circuit boards is that they're "printed" circuit boards. The pattern that will eventually be etched into the copper foil is created using a light-sensitive film. This video shows it step-by-step

Complex electronics have many layers. They print and etch a layer, glue on another layer of fiberglass, copper, and photoresist, and print the next trace layer. The final layers of solder-mask and symbols or letters are silk-screen printed - almost exactly like t-shirts.

An electronic device involves lots of different chips, components (resistors / capacitors), connectors, and so on -- maybe dozens or even hundreds of parts. The parts have pins or wires sticking out of them that need to be electrically connected. (Some chips have a couple dozen connection pins.)

A circuit board is a sturdy plastic / fiberglass surface on one side, copper on the other side [1]. A "new" circuit board has a solid copper surface on the back, coated with a light-sensitive protective chemical.

A solid surface is no good though. As a circuit designer you don't want everything connected to everything else, you want to make connections between specific points only.

So to get the connections you want, you make a shadow over the parts of the copper you want to keep, then turn on a bright light, then wash the copper with acid. The acid dissolves the copper, but only where the light destroyed the protective chemical.

Now you just have to:

• Put your components in the right places on the fiberglass side
• Drill holes for the wires / pins
• Glue ("solder") the wires / pins to the copper with a tiny bit of molten metal

After soldering, the parts are mechanically locked in place, electrically connected where they should be and insulated everywhere else.

There are many circuit board customization companies that offer these services for very cheap prices. You send your circuit design files to the company, and they use specialized robots to wash the copper, drill the holes, and also print directly on the board whatever graphics / labels you want ("silkscreening"). They ship you the finished circuit boards by mail / UPS / Fedex like any other online delivery. For an additional fee, another specialized robot can place the components and solder them for you ("pick and place") [2].

You can buy one or a few circuit boards with a unique circuit design for a prototype or a hobbyist one-off. Or you can order hundreds or thousands of identical boards at a time, if you're making a mass produced commercial product.

[1] Circuit boards can also have multiple layers.

[2] A lot of modern electronics use components ("SMT") that have very small, closely spaced connection points. These components are really designed to be soldered by robots; it's difficult for a human to solder them by hand.

> a plastic board covered in fibreglass

The board is the fiberglass+resin. Usually. That is called FR-4. Sometimes you see ultra cheap boards that use paper and resin (FR-2) substrate. On top of that is one or two layers of copper foil, glued down, then after etching the traces it is coated with UV setting liquid plastic called solder resist.