In the root of the directory you can run the test or the program.
clj -M -m org.cwt.coreclj -M -m org.cwt.core -hclj -M -m org.cwt.core -n 5
When jacking in (Ctrl+Shift+P then "Calva: Start a Project REPL and Connect ...") using the Calva extension, select deps.edn and then tick the dev checkbox. Then open core.clj in the editor and use the extension again, now with "Calva: Load/Evaluate Current File ...". Now it should be possible to send snippets to the REPL and have the results appear in the editor. (Place the cursor at the end of line 11 and hit Alt+Return and some numbers should appear.)
clj -M:testto run all tests once.clj -M:test --watchto continuously look for changes and re-run tests.
clj -M:outdated will check for outdated dependencies in deps.edn.