The Podfile

Using the files from a folder local to the machine.

If you would like to develop a Pod in tandem with its client project you can use :path.

pod 'Alamofire', :path => '~/Documents/Alamofire'

From a podspec in the root of a library repo.

Sometimes you may want to use the bleeding edge version of a Pod, a specific revision or your own fork. If this is the case, you can specify that with your pod declaration.

To use the master branch of the repo:
pod 'Alamofire', :git => 'https://github.com/Alamofire/Alamofire.git'

The podspec file is expected to be in the root of the repo, if this library does not have a podspec file in its repo yet, you will have to use one of the approaches outlined in the sections below.

转载：
https://guides.cocoapods.org/using/the-podfile.html