You just created a new madlib project, if it's your first project you should read the following.
Madlib is a general purpose programming language that compiles to Javascript. It means that you need to have Nodejs installed and configured in order to make it work. Madlib can target nodejs or browser, by default it will compile for nodejs.
First, you need to compile the program. For node:
madlib compile -i src/Main.mad
Then, you can run it like this:
node build/Main.mjs
As a native binary:
madlib compile --target llvm -i src/Main.mad -o ./build/helloWorld
Then, you can run it like this:
./build/helloWorld