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> 
} 

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 
}