Split string with PowerShell and do something with each token

"Once upon a time there were three little pigs".Split(" ") | ForEach {
    "$_ is a token"
 }

The key is $_, which stands for the current variable in the pipeline.

About the code you found online:

% is an alias for ForEach-Object. Anything enclosed inside the brackets is run once for each object it receives. In this case, it’s only running once, because you’re sending it a single string.

$_.Split(" ") is taking the current variable and splitting it on spaces. The current variable will be whatever is currently being looped over by ForEach.