With the installation steps done, you should be able start from any exercise directory (e.g., ~/exercism/gdscript/two-fer) and run the script (living one level up, in ../) to test your local solution to that exercise:
../test-local-gdscript-solution.shSolving an exercise means making all its tests pass.
To help you get started, each exercise comes with a GDScript file named after the exercise (e.g., exercism/gdscript/two-fer/two_fer.gd).
You can use this file as a starting point for building your solution.
Feel free to change it as needed, but the tests expect the function names to be as originally provided.