Behind a noun:

• amount + ずつ + predicate  = each, at a time, per unit
毎日30分ずつ運動をします。I exercise 30 minutes everyday.
三人ずつ (の)グループを作ってください。Please make a group of three.
全部の漢字を5回ずつ書きなさい。Write all the kanji, five times each.
 

※ずつ emphasizes repetition.  Without it, each sentence will mean the same thing without the emphasis.