For

Run a command block based on a conditional test.

Syntax
      for (init; condition; repeat) 
        {command_block}

Key

   init      Commands, separated by commas, to run before the loop begins.
             Typically used to initialize a variable with a starting value.

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

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

A typical use of the for loop is to operate on a subset of the values in an array.
In most cases, if you want to iterate all values in an array, consider using a foreach statement.

Examples

Count to 10:

 PS> for($i=1; $i -le 10; $i++){Write-Host $i}

You can use carriage returns instead of semi-colons:

 PS> for($i=1
     $i -le 10
     $i++){
       Write-Host $i
     }

“An essential aspect of creativity is not being afraid to fail” ~ Edwin Land

Related:

Break statement
Continue statement
comparison_operators
ForEach - Loop through values in the pipeline
IF - Conditionally perform a command
While Loop while a condition is True