These are the Harvester (or, as the more observant may have registered, a scythe) and a Feeder. Once crafted you place them on your homestead (if you have any space left at all...) ready to be used.
Once you've decided where you're going to use your tool click on it to bring up it's menu:
Pick "Use" and simply select a group of up to five crops (for the Harvester) or animals (with the feeder) and click on them in much the same way as hiring a friend or using the Fast Hands Boost.
Please note, UNLIKE the fast hands boost using a tool consumes the normal amount of energy so up to five points each click. It can also be used again and again as the tools are permanent.
With animals try to group them together as the feeder has a radius effect just like hiring does so needs the animals to be near each other.
Then just sit back and enjoy all the extra time you've got on your hands thanks to your labour saving devices! Can I suggest surfing our site? ;)