To use ifttt’s own description you can use ifttt to create tasks with the following structure: when something happens (this) then do something else (that).
I think this is best illustrated with some of the recipes that I use.
I really like my Kindle and using an ifttt task I now get an automatic email when a new book is added to the top 100 free ebooks.
I have various Gmail tasks, for example if I star an email it is automatically sent to Evernote.
Always liking the idea of a backup plan – all my Diigo bookmarks are sent automatically to Evernote (I also have Diigo set up to send the bookmarks to Delicious!)
There are numerous channels to use as building blocks for tasks.
You can use the numerous supplied recipes as a basis for your own tasks or create tasks from scratch. Ifttt has worked flawlessly since I started using it - I am very impressed!