The first thing you should do is to have install clasp from google
npm install -g @google/clasp
clasp login
clasp create
Eventually when you are done coding, can push the code to Apps Script using:
clasp push
Important
Above method is all for developing apps script code using javascript locally. To develop on Apps Script platform please refer the official documentations.
Tip
If you have any Notion related questions, try asking in discord!