If this then that (IFTTT). It's a service that connects one service to another with actions on specific elements of those services. So, for example, I can tag an image I've just uploaded to Flickr and automatically have a blog post created with that image. Or Add item tagged readability in Feedly or Google Reader to Readability to my Readability reading list.
IFTTT calls a service a channel and connecting services is creating a recipe. There are about 60 channels and quite a few canned recipes you can use right away. However, I chose to create my own to have more control.
Before a recipe can be created each associated channel must first be activated. Activating a channel simply means logging into that service and via IFTTT and giving permissions to access the service. Once a channel is activated it can be used in a recipe. Creating a recipe means selecting a trigger channel and trigger – this – and the destination channel action – that – along with various ingredients. Once your recipe is created you can activate it. I'm bit sure of the timing of recipes. I don't know if they run every hour, half hour etc. Recipes can be edited later and even shared publicly for others to use.
There isn't much more to say. The service is quite easy to use.