Log into KiSSFLOW. See How to Access KiSSFLOW for more information on that.

Once you are logged into KiSSFLOW, click on the large red + icon located in the lower right of the window.

Click on Initiate next to Purchase Order & Check Request. You may have to scroll down to find it or you can type "purchase" in the search box.

Filll out the form as needed. Make sure to add at least one row under the Purchase Order and Check Request Details section.
 

Click on the Submit button at the bottom of the screen to submit your request.