How to listen to user touches for UICollectionViewCell in iOS?

Swift 5

didSelectItemAtIndexPath has been renamed to didSelectItemAt in Swift 5

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
         //Do your logic here

    }

You should implement UICollectionViewDelegate protocol method collectionView(_:didSelectItemAtIndexPath:). When you press one of your collection view cells this method get called. Here is sample implementation

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    let url = thumbnailFileURLS[indexPath.item]
    if UIApplication.sharedApplication().canOpenURL(url) {
        UIApplication.sharedApplication().openURL(url)
    }
}

By the way I don't know where you get url. So I improvised a bit :)