Wolfram|Alpha doesn't do this. It's meant for natural language processing. It can handle some Wolfram Language code - mostly just the more common expressions that people tend to use.

If you want to execute Wolfram Language Code, I would check out Mathematica Online.

There is no strict documentation for Wolfram|Alpha like there would be for a programming language. Instead there's a list of example inputs for different areas of interest. This fits with how it was meant to be used.

I would not use it for Wolfram Language Code. It wasn't really designed for that purpose. The Wolfram Language is implemented in Mathematica and Mathematica online.