Do

Run a command block based on the results of a conditional test.

Syntax
      [:Loop_label] Do
      {
         command_block
      } while (condition)

or

      [:Loop_label] Do
      {
         command_block
      } until (condition)

Key

   condition      If this evaluates to TRUE the loop {command_block} runs.
                  when the loop has run once the condition is evaluated again

   command_block  Commands, separated by commas, to run each time the loop repeats.

   :Loop_label    An optional label than can be used to break or continue.

A While loop continues as long as the condition is TRUE.
An Until loop continues as long as the condition is FALSE. Until is an antonym of While.

As long as the condition is met, PowerShell will continue to rerun the {command_block} section unless interrupted by a break or continue statement.

Examples

Count to 10:

 PS> Do { $val++ ; Write-Host $val } while($val -ne 10)

You can use carriage returns instead of semi-colons:

 PS> Do { $val++ 
          Write-Host $val
        } while($val -ne 10)

“A quarrel is quickly settled when deserted by one party; there is no battle unless there be two” ~ Lucius Annaeus Seneca

Related:

Break statement
Continue statement
ForEach-Object - Loop for each object in the pipeline (foreach)
ForEach - Loop through values in the pipeline
IF - Conditionally perform a command
For - Loop through items that match a condition
Switch - Multiple if statements
While - Loop while a condition is True