This is not a required change. If you are not interested in adding the "Projected Ship Date" section to the order complete/summary page, you do not need any change to your custom skin. Your site will function just as before.
Adding Projected ship date to order complete/summary page
1. Check if your custom skin has a layout file called "ordersummarylayout.txt"
If "ordersummarylayout.txt" exists in your custom skin root folder, continue step 2. Otherwise you do not need any change here.
2. Add new PROJECTEDDELIVERY skin tag
Open "ordersummarylayout.txt" and insert
@@@PROJECTEDDELIVERY:<div class="col-md-6 order-summary-item-projectdelivery"><div class="well"> :</div></div>@@@
after @@@REQUESTEDDELIVERY .....@@@