This is a library you run on your FPGA.

When you are making a circuit board, you can make a big pad of exposed copper and connect it to one of the I/O pins on the chip.

You can then use that pad as a button, instead of buying a button and soldering it to the board

But don't do this unless you have to, since a button is a hundred times more reliable and easier to use. (Buttons actually provide tactile feedback, for one....)

can't you provide electrical feedback?

In terms of stuff lighting up? Sure. In terms of something the finger pressing the button can feel, no. It's completely impossible with a cap-touch button, a problem also shared with piezo buttons. And a major reason they are very annoying to use.

I feel like I saw this concept recently (big exposed conductive pads) as a way to generate random numbers (Ben Heck's recent YT video about his lanyard game).