Well you can actually build something yourself. Sure, someone else built e.g. the code editor you‘re using, but if you come up with an algorithm yourself, you did, by definition, build it yourself.
If you create an algorithm, it is likely based on previous algorithms you learned, and millenia of mathametics.
To implement it in a computer, you likely rely on an operating system to run on, layers of userspace libraries, layers of firmware, many independent hardware components. An electrical supply.
To implement it in a computer, you likely rely on an operating system to run on, layers of userspace libraries, layers of firmware, many independent hardware components. An electrical supply.