Okay this one is straight forward, here are the parts of a typical mechanical keyboard from top to bottom physically.
Keycaps, switches, plate, PCB, and case.
Keycaps are the first thing you see on the keyboard, they are the piece of plastic with alphabets and numbers on them that u press. Typically in black or white but comes in much more colors in the custom world. Click here to read more on keycaps.
Switches are literally what the name implies, they switch the keys on or off, so when you press “W” it literally turns on W on the electronic circuit board to send the signal to your computer or phone. There are 3 types in general + silent variants. Read more about switches here and here.
The plate is used to hold the switches in the right place, and in customs we use different materials for different sounds and typing feel. However, not every keyboard has a plate, as many gaming keyboards use an “integrated plate” where the plate and case are a single component to save costs and results in a keyboard that doesn’t sound very good. Read more about keyboard plates here.
This is straightforward, it’s basically just a circuit board that turns your key press into something your computer recognizes and sometimes make really pretty lights too.