As the condition for a while loop comes first, the body of the loop will only execute if the condition evaluates to true:
while (<condition>) { <body-statements> }
For example, a while loop may be used to wait for something to happen. For example, it might be used to wait for a path to exist:
while (-not (Test-Path $env:TEMP est.txt -PathType Leaf)) { Start-Sleep -Seconds 10 }