This blog includes how to display banner ads for DFP users.For this first user need to signed up as a DFP (Double click for publisher) and then install cocoa pods for Google mobile ads.

pod 'Google-Mobile-Ads-SDK'

We can also include the SDK manually but using pod is the best way.

After that in your view controller use the following properties-

@import GoogleMobileAds;

@interface ViewController ()<GADBannerViewDelegate>{
      BOOL _bannerIsVisible;
}
@property (strong, nonatomic)  DFPBannerView  *bannerView;
@end

After this initialize the banner view in viewdidload-

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    _bannerView = [[DFPBannerView alloc] initWithFrame:CGRectMake(0, [UIScreen mainScreen].bounds.size.height, [UIScreen mainScreen].bounds.size.width, 50)];
    [self.view addSubview:_bannerView];
    //set the ad unit id
    self.bannerView.adUnitID = @"/31930164/Your-banner-key";
    self.bannerView.rootViewController = self;
    [self.bannerView loadRequest:[DFPRequest request]];
    //set delegate
    [self.bannerView setDelegate:self];
}

then use the delegates of banner view-

- (void)adViewDidReceiveAd:(GADBannerView *)bannerView{
    if (!_bannerIsVisible)
    {

    if (bannerView.superview == nil){

        [self.view addSubview:bannerView];
    }

        [UIView beginAnimations:@"animateAdBannerOn" context:NULL];
        
        // Assumes the banner view is just off the bottom of the screen.
        bannerView.frame = CGRectOffset(bannerView.frame, 0, -bannerView.frame.size.height);
        CGRect frame = self.view.frame;
        frame.size.height = bannerView.frame.origin.y;
        self.view.frame = frame;
        [UIView commitAnimations];
        
        _bannerIsVisible = YES;
    }
}

- (void)adView:(GADBannerView *)bannerView didFailToReceiveAdWithError:(GADRequestError *)error{
    NSLog(@"Failed to retrieve ad  %@",error.description);
    
    if (_bannerIsVisible)
    {
        [UIView beginAnimations:@"animateAdBannerOff" context:NULL];
        
        // Assumes the banner view is placed at the bottom of the screen.
        bannerView.frame = CGRectOffset(bannerView.frame, 0, bannerView.frame.size.height);
        CGRect frame = self.view.frame;
        frame.size.height = bannerView.frame.origin.y;
        self.view.frame = frame;
        
        [UIView commitAnimations];
        
        _bannerIsVisible = NO;
    }

}