The RxSwift library extends Swift with an extensive set of features for functional reactive programming inspired by the Reactive Extensions for .NET.
Michael Ciurus has written a great set of tutorials for those starting out with RxSwift called RxSwift for Dummies allowing you to develop an understanding of functional reactive programming, and also in using the RxSwift library through an extensive series of explanations and examples.
Michael has also written an RxSwift Safety Manual to help avoid any unwanted side effects when using RxSwift which he wrote after a number of months of using RxSwift.
You can find the RxSwift Safety Manual on the Swift Pearls site here.
A great series of tutorials for those looking to use RxSwift.