Here's a few images I found on Google:
The stretchers actually rested and interlocked onto an assembly tied to the landing skids. The litter was latch the framework and the soldier strapped to the litter to keep them from slipping or falling. The shield was to protect the passengers eyes and allow for "normal" breathing. The downwash of the rotors would otherwise impede someones breathing who was in shock or laboring to do so.
The bellows enclosed litters were useful in the winter time to keep the soldier warm, but were a cumbersome affair. Hence, the switch to using enclosed cargo helos such as the UH-19 and eventually the famous Huey.