Make sure you have yarn installed. (Currently we are just using yarn v1. When v2 is more stable we can consider upgrading).
yarn install
yarn start
For development, using the vs-code reason plugin your code should reload on every save.
If however you don't use such a plugin you can still watch for file changes using the following command. (Sometimes it is useful to do this to see what is happening in the terminal.)
run re:watch
Sometimes VsCode stops working properly. In this case you can run <ctrl+shift+p> and then either Developer: Reload Window or Restart Reason Language Server. Another thing that you can do is run npm run re:build (which rebuilds everything, and might fix any buggy vscode behaviour.)
yarn run build
yarn run test