This puts an icon called 'WhileLoop' in the Object Catalog (under the Widgets tab) in the Scripting category. To use the while loop, drag the icon into a morphic script and then drag the commands you want into it (in the same way as using the Test-Yes-No icon in the top-bar of morphic scripts).
Typically you might have set a variable to an initial value before entering the while loop; each time round the loop you cause the variable to be incremented so the test will check the value of the variable to make sure that is still less than or equal to some maximum value. If the result of the test is 'true' that will cause the loop to be repeated.