2 projects to kickstart your development with the @pnp/sp-taxonomy library.
The classic sample transpiles typescript into a js file to be included as per old school if you're into on prem development or for some other reason needs to build for classic sites.
A SPFx webpart, nothing fancy just the standard yeoman react template but with the taxonomy sample code
Put your taxonomy id's into the code, build and run. The code will add a term to the term set you provided and then output to the console when succesful. Not very useful but VERY nice and clean programming against the taxonomy!